Return a value from default progress report function

The progress reporting function returns a boolean. The returned
value is never used by the tesseract and its meaing is not
documented, which renders the value meaningless. Still, lack of
return should not be premitted.

src/ccutil/ocrclass.h

@@ -174,8 +174,9 @@ private:
                                     int bottom)
   {
     if ( ths->progress_callback ) {
-      (*(ths->progress_callback))(ths->progress, left, right, top, bottom);
+      return (*(ths->progress_callback))(ths->progress, left, right, top, bottom);
     }
+    return true;
   }
 
 };