mcstrans: free constraint in error branch

Free constraint, like in all other error branches.

Reported-by: Cppcheck
Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Acked-by: James Carter <jwcart2@gmail.com>

mcstrans/src/mcstrans.c

@@ -477,6 +477,7 @@ add_constraint(char op, char *raw, char *tok) {
 		}
 		if (asprintf(&constraint->text, "%s%c%s", raw, op, tok) < 0) {
 			log_error("asprintf failed %s", strerror(errno));
+			free(constraint);
 			return -1;
 		}
 		constraint->op = op;