lbmsrs: Fix bug in heuristic causing malformed packet.

Change-Id: Ib3faa627fadb56833df0f37debeab1f8f0fe2042
Reviewed-on: https://code.wireshark.org/review/37410
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

epan/dissectors/packet-lbmsrs.c

@@ -852,6 +852,10 @@ static gboolean check_lbmsrs_packet(tvbuff_t *tvb, guint offset)
         offset += 3;
         /*move the offset by the metadata length*/
         offset += rsocket_metadata_len;
+        if (tvb_length < (offset - start_offset + 6))
+        {
+            return FALSE;
+        }
     }