Fix #146281: Overlay: Uninitialized data in Paint Mask

The early out case did not initialize the data.

This caused garbage data to be used for the visibility
flag, producing inconsistent result.

Pull Request: https://projects.blender.org/blender/blender/pulls/146704

source/blender/draw/intern/mesh_extractors/extract_mesh_vbo_paint_overlay_flag.cc

@@ -19,6 +19,7 @@ static void extract_paint_overlay_flags(const MeshRenderData &mr, MutableSpan<in
     selection = mr.select_vert;
   }
   if (selection.is_empty() && mr.hide_poly.is_empty() && (!mr.edit_bmesh || !mr.orig_index_vert)) {
+    flags.fill(0);
     return;
   }
   const OffsetIndices faces = mr.faces;