fix segfault when using preserved stx prop with non-interned-symbol key

closes #1594

pkgs/racket-test-core/tests/racket/stx.rktl

@@ -2468,6 +2468,12 @@
   (check-bad (read (open-input-string "#0=(1 . #0#)")))
   (check-bad void))
 
+(err/rt-test (syntax-property #'+ 1 #'+ #t)
+             (lambda (exn)
+               (regexp-match
+                #rx"expected an interned symbol key for a preserved property"
+                (exn-message exn))))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Make sure the srcloc encoding doesn't do something strange
 ;; with a path in a root directory:

racket/src/racket/src/syntax.c

@@ -8229,7 +8229,7 @@ static Scheme_Object *syntax_property(int argc, Scheme_Object **argv)
   if ((argc > 3) && SCHEME_TRUEP(argv[3])) {
     if (!SCHEME_SYMBOLP(argv[1]) || SCHEME_SYM_WEIRDP(argv[1]))
       scheme_contract_error("syntax-property",
-                            "expected an interned symbol key for a preserved property"
+                            "expected an interned symbol key for a preserved property",
                             "given", 1, argv[1],
                             NULL);
   }