core: add missing return after call to gui_buffer_unmerge_all()

src/core/wee-command.c

@@ -654,6 +654,7 @@ COMMAND_CALLBACK(buffer)
             if (string_strcasecmp (argv[2], "-all") == 0)
             {
                 gui_buffer_unmerge_all ();
+                return WEECHAT_RC_OK;
             }
             else
             {