avcodec/h261dec: Fix UB NULL + 0, remove broken resync code

last_resync_gb is never initialized, causing NULL + 0
in align_get_bits(). In addition to that, the loop is never
entered.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/h261dec.c

@@ -172,7 +172,7 @@ static int h261_decode_gob_header(H261DecContext *h)
 static int h261_resync(H261DecContext *h)
 {
     MpegEncContext *const s = &h->s;
-    int left, ret;
+    int ret;
 
     if (h->gob_start_code_skipped) {
         ret = h261_decode_gob_header(h);
@@ -185,22 +185,6 @@ static int h261_resync(H261DecContext *h)
                 return 0;
         }
         // OK, it is not where it is supposed to be ...
-        s->gb = s->last_resync_gb;
-        align_get_bits(&s->gb);
-        left = get_bits_left(&s->gb);
-
-        for (; left > 15 + 1 + 4 + 5; left -= 8) {
-            if (show_bits(&s->gb, 15) == 0) {
-                GetBitContext bak = s->gb;
-
-                ret = h261_decode_gob_header(h);
-                if (ret >= 0)
-                    return 0;
-
-                s->gb = bak;
-            }
-            skip_bits(&s->gb, 8);
-        }
     }
 
     return -1;