Fix RegExp.prototype.compile error case

test/mjsunit/regexp-compile.js

Index: test/mjsunit/regexp-compile.js
diff --git a/test/mjsunit/regexp-compile.js b/test/mjsunit/regexp-compile.js
index 92c3f7b3dd62e5c69f38f9fbe0c071b96c1ec693..f00178008ccaede68a6a62b6edf4dcf5ee16b4cb 100644
--- a/test/mjsunit/regexp-compile.js
+++ b/test/mjsunit/regexp-compile.js
@@ -42,3 +42,7 @@ re.compile("(y)");
 assertEquals(["y", "y"], re.exec("axyb"));
 
 assertEquals(2, re.compile.length);
+
+// If RegExp parsing fails, the RegExp is not modified
+var r = /./; try { r.compile('? invalid'); } catch(err){}
+assertEquals("/./", r.toString());