branches/zip: row_merge_sort_linked_list(): Add a default: ut_error; branch

to the switch (row_merge_cmp(...)) to eliminate bogus warning about
uninitialized variable tmp.

row/row0merge.c

@@ -648,6 +648,8 @@ row_merge_sort_linked_list(
 						list2_size = 0;
 					}
 					break;
+				default:
+					ut_error;
 				}
 
 				/* Append the element to the merged list */