Fixed memory leak in error branch of parsestrplus. CID 715374 Variable s going…

Fixed memory leak in error branch of parsestrplus. CID 715374 Variable s going out of scope leaks the storage it points to.

Python/ast.c

@@ -3846,6 +3846,7 @@ parsestrplus(struct compiling *c, const node *n, int *bytesmode)
                 goto onError;
             if (*bytesmode != subbm) {
                 ast_error(c, n, "cannot mix bytes and nonbytes literals");
+                Py_DECREF(s);
                 goto onError;
             }
             if (PyBytes_Check(v) && PyBytes_Check(s)) {