Fix #34633: Merge First/Last crashes Blender

It was check happening when generating menu with available modes
for merge operator, but no checks happened when executing operator.

Since operator could be called from python or shortcut, it was
possible to bypass all the checks.

1 files changed, 10 insertions, 0 deletions

diff --git a/source/blender/editors/mesh/editmesh_tools.c b/source/blender/editors/mesh/editmesh_tools.c
index 39a5ac534d3..148c6c413d0 100644
--- a/source/blender/editors/mesh/editmesh_tools.c
+++ b/source/blender/editors/mesh/editmesh_tools.c
@@ -2160,12 +2160,22 @@ static int merge_firstlast(BMEditMesh *em, int first, int uvmerge, wmOperator *w
 	BMVert *mergevert;
 	BMEditSelection *ese;
 
+	/* operator could be called directly from shortcut or python,
+	 * so do extra check for data here
+	 */
+
 	/* do sanity check in mergemenu in edit.c ?*/
 	if (first == 0) {
+		if (!em->bm->selected.last || ((BMEditSelection *)em->bm->selected.last)->htype != BM_VERT)
+			return OPERATOR_CANCELLED;
+
 		ese = em->bm->selected.last;
 		mergevert = (BMVert *)ese->ele;
 	}
 	else {
+		if (!em->bm->selected.first || ((BMEditSelection *)em->bm->selected.first)->htype != BM_VERT)
+			return OPERATOR_CANCELLED;
+
 		ese = em->bm->selected.first;
 		mergevert = (BMVert *)ese->ele;
 	}