regcomp: propagate allocation failures

The error code of an allocating function was not checked in tre_add_tag.

src/regex/regcomp.c

@@ -1584,6 +1584,7 @@ tre_add_tags(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *tree,
 		  {
 		    status = tre_add_tag_right(mem, left, tag_left);
 		    tnfa->tag_directions[tag_left] = TRE_TAG_MAXIMIZE;
+		    if (status == REG_OK)
 		      status = tre_add_tag_right(mem, right, tag_right);
 		    tnfa->tag_directions[tag_right] = TRE_TAG_MAXIMIZE;
 		  }