tap_export_pdu: free err_info for WTAP_ERR_INTERNAL.

WTAP_ERR_INTERNAL also returns an err_info script describing the
internal error, so it should be freed to avoid leaking it.

ui/tap_export_pdu.c

@@ -73,6 +73,10 @@ export_pdu_packet(void *tapdata, packet_info *pinfo, epan_dissect_t *edt, const
             g_free(err_info);
             break;
 
+        case WTAP_ERR_INTERNAL:
+            g_free(err_info);
+            break;
+
         default:
             break;
         }