Merge pull request #24581 from vrabaud:tsan

Fix race condition in color_lab.cpp initLabTabs(). #24581

There is a race condition between when the static bool is initialized (which is thread safe) and its value check. This PR changes the static bool to a static lambda call to make it thread safe. The static_cast<void> in the end is to prevent unused variables warnings.

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work

modules/imgproc/src/color_lab.cpp

@@ -1223,11 +1223,8 @@ static LABLUVLUT_s16_t initLUTforLABLUVs16(const softfloat & un, const softfloat
 }
 
 
-static void initLabTabs()
+static bool createLabTabs()
 {
-    static bool initialized = false;
-    if(!initialized)
-    {
     softfloat f[LAB_CBRT_TAB_SIZE+1], g[GAMMA_TAB_SIZE+1], ig[GAMMA_TAB_SIZE+1];
     softfloat scale = softfloat::one()/softfloat(LabCbrtTabScale);
     int i;
@@ -1333,9 +1330,13 @@ static void initLabTabs()
             }
         }
     }
+    return true;
+}
 
-        initialized = true;
+static bool initLabTabs()
-    }
+{
+    static bool initialized = createLabTabs();
+    return initialized;
 }