Fix/workaround 'convert object' messing up linked data.

'Convert To...' Object operation has very weird effect of actually
working at obdata level, not object level, which means *all* objects
(even unselected/hidden/in other scenes/...) using same obdata will be
converted to new selected type.

IMHO this is very bad behavior, but... not a bug really, so do not
change this for now.

But at least, do not do that when working on some linked data, else it
leaves Blend file in invalid (incoherent) state until next reload.

So workaround for now is to enforce the 'Keep Original' option when some
linked object/obdata is affected by the operation.

Also fixed somewhat broken usercount handling in Curve->Mesh part.

1 files changed, 5 insertions, 4 deletions

diff --git a/source/blender/blenkernel/intern/mesh.c b/source/blender/blenkernel/intern/mesh.c
index 89e988782d2..171ae4485a0 100644
--- a/source/blender/blenkernel/intern/mesh.c
+++ b/source/blender/blenkernel/intern/mesh.c
@@ -1398,9 +1398,7 @@ void BKE_mesh_from_nurbs_displist(Object *ob, ListBase *dispbase, const bool use
 	cu->mat = NULL;
 	cu->totcol = 0;
 
-	if (ob->data) {
-		BKE_libblock_free_us(bmain, ob->data);
-	}
+	/* Do not decrement ob->data usercount here, it's done at end of func with BKE_libblock_free_us() call. */
 	ob->data = me;
 	ob->type = OB_MESH;
 
@@ -1410,11 +1408,14 @@ void BKE_mesh_from_nurbs_displist(Object *ob, ListBase *dispbase, const bool use
 		if (ob1->data == cu) {
 			ob1->type = OB_MESH;
 		
+			id_us_min((ID *)ob1->data);
 			ob1->data = ob->data;
-			id_us_plus((ID *)ob->data);
+			id_us_plus((ID *)ob1->data);
 		}
 		ob1 = ob1->id.next;
 	}
+
+	BKE_libblock_free_us(bmain, cu);
 }
 
 void BKE_mesh_from_nurbs(Object *ob)