Fix T68103: bevel sometimes infinite loops with patch miter.

Needed to null terminate list of chain to process width adjustments on.

source/blender/bmesh/tools/bmesh_bevel.c

@@ -3122,6 +3122,7 @@ static void adjust_offsets(BevelParams *bp, BMesh *bm)
       }
       if (!iscycle) {
         /* right->left direction, changing vchainstart at each step */
+        v->adjchain = NULL;
         v = vchainstart;
         bvcur = bv;
         do {