Fix use after free

src/textures.c

@@ -677,7 +677,7 @@ void ImageFormat(Image *image, int newFormat)
             Color *pixels = GetImageData(*image);
 
             free(image->data);      // WARNING! We loose mipmaps data --> Regenerated at the end...
-
+            image->data = NULL;
             image->format = newFormat;
 
             int k = 0;
@@ -824,12 +824,13 @@ void ImageFormat(Image *image, int newFormat)
             }
 
             free(pixels);
-            
+            pixels = NULL;
             // In case original image had mipmaps, generate mipmaps for formated image
             // NOTE: Original mipmaps are replaced by new ones, if custom mipmaps were used, they are lost
             if (image->mipmaps > 1)
             {
                 image->mipmaps = 1;
+		assert(image->data != NULL);
                 ImageMipmaps(image);
             }
         }