Fix #106998: selection of bones in grease pencil weightpaint mode fails

Caused by 2eeec49640.

Above commit would early out when falling through the specialized
greasepencil selection operator to view3d_select_exec. But in order to
select posebones in grease pencil weightpaint mode, we still have to
continue with view3d_select_exec.

Now check this special case [with convenient
`BKE_object_pose_armature_get_with_wpaint_check`] and DONT early out in
that case.

Should go into 3.3 LTS as well.

Pull Request: https://projects.blender.org/blender/blender/pulls/107076

source/blender/editors/space_view3d/view3d_select.cc

@@ -3088,12 +3088,13 @@ static int view3d_select_exec(bContext *C, wmOperator *op)
   Object *obedit = CTX_data_edit_object(C);
   Object *obact = CTX_data_active_object(C);
 
-  if (obact && obact->type == OB_GPENCIL_LEGACY && GPENCIL_ANY_MODE((bGPdata *)obact->data)) {
-    /* Prevent acting on Grease Pencil (when not in object mode), it implements its own selection
-     * operator in other modes. We might still fall trough to here (because that operator uses
-     * OPERATOR_PASS_THROUGH to make tweak work) but if we don't stop here code below assumes we
-     * are in object mode it might falsely toggle object selection. Alternatively, this could be
-     * put in the poll function instead. */
+  if (obact && obact->type == OB_GPENCIL_LEGACY && GPENCIL_ANY_MODE((bGPdata *)obact->data) &&
+      (BKE_object_pose_armature_get_with_wpaint_check(obact) == nullptr)) {
+    /* Prevent acting on Grease Pencil (when not in object mode -- or not in weight-paint + pose
+     * selection), it implements its own selection operator in other modes. We might still fall
+     * trough to here (because that operator uses OPERATOR_PASS_THROUGH to make tweak work) but if
+     * we don't stop here code below assumes we are in object mode it might falsely toggle object
+     * selection. Alternatively, this could be put in the poll function instead. */
     return OPERATOR_PASS_THROUGH | OPERATOR_CANCELLED;
   }