Use NGX_CONF_OK in some function return checks.

The functions ngx_http_merge_types() & ngx_conf_merge_path_value()
return either NGX_CONF_OK aka NULL aka ((void *)0) (probably) or
NGX_CONF_ERROR aka ((void *)-1).

They don't return an integer constant which is what NGX_OK aka (0) is.

Lets use the right thing in the function return check.

This was found with -Wzero-as-null-pointer-constant which was enabled
for C in GCC 15 (not enabled with Wall or Wextra... yet).

Link: <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117059>

src/http/modules/ngx_http_addition_filter_module.c

@@ -245,7 +245,7 @@ ngx_http_addition_merge_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_http_merge_types(cf, &conf->types_keys, &conf->types,
                              &prev->types_keys, &prev->types,
                              ngx_http_html_default_types)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/modules/ngx_http_charset_filter_module.c

@@ -1564,7 +1564,7 @@ ngx_http_charset_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_http_merge_types(cf, &conf->types_keys, &conf->types,
                              &prev->types_keys, &prev->types,
                              ngx_http_charset_default_types)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/modules/ngx_http_fastcgi_module.c

@@ -3130,7 +3130,7 @@ ngx_http_fastcgi_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_conf_merge_path_value(cf, &conf->upstream.temp_path,
                               prev->upstream.temp_path,
                               &ngx_http_fastcgi_temp_path)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/modules/ngx_http_gzip_filter_module.c

@@ -1115,7 +1115,7 @@ ngx_http_gzip_merge_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_http_merge_types(cf, &conf->types_keys, &conf->types,
                              &prev->types_keys, &prev->types,
                              ngx_http_html_default_types)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/modules/ngx_http_proxy_module.c

@@ -3859,7 +3859,7 @@ ngx_http_proxy_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_conf_merge_path_value(cf, &conf->upstream.temp_path,
                               prev->upstream.temp_path,
                               &ngx_http_proxy_temp_path)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/modules/ngx_http_scgi_module.c

@@ -1543,7 +1543,7 @@ ngx_http_scgi_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_conf_merge_path_value(cf, &conf->upstream.temp_path,
                                   prev->upstream.temp_path,
                                   &ngx_http_scgi_temp_path)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/modules/ngx_http_ssi_filter_module.c

@@ -2942,7 +2942,7 @@ ngx_http_ssi_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_http_merge_types(cf, &conf->types_keys, &conf->types,
                              &prev->types_keys, &prev->types,
                              ngx_http_html_default_types)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/modules/ngx_http_sub_filter_module.c

@@ -901,7 +901,7 @@ ngx_http_sub_merge_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_http_merge_types(cf, &conf->types_keys, &conf->types,
                              &prev->types_keys, &prev->types,
                              ngx_http_html_default_types)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/modules/ngx_http_uwsgi_module.c

@@ -1803,7 +1803,7 @@ ngx_http_uwsgi_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_conf_merge_path_value(cf, &conf->upstream.temp_path,
                                   prev->upstream.temp_path,
                                   &ngx_http_uwsgi_temp_path)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/modules/ngx_http_xslt_filter_module.c

@@ -1112,7 +1112,7 @@ ngx_http_xslt_filter_merge_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_http_merge_types(cf, &conf->types_keys, &conf->types,
                              &prev->types_keys, &prev->types,
                              ngx_http_xslt_default_types)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }

src/http/ngx_http_core_module.c

@@ -3931,7 +3931,7 @@ ngx_http_core_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     if (ngx_conf_merge_path_value(cf, &conf->client_body_temp_path,
                               prev->client_body_temp_path,
                               &ngx_http_client_temp_path)
-        != NGX_OK)
+        != NGX_CONF_OK)
     {
         return NGX_CONF_ERROR;
     }