Protect the RegExp against early garbage collection

Backported from Qt 5.5

Change-Id: Ice9fd8061fac0c35d787e1603873c69f8ef7e10b
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>

src/qml/jsruntime/qv4regexpobject.cpp

@@ -286,7 +286,7 @@ ReturnedValue RegExpCtor::construct(Managed *m, CallData *callData)
         }
     }
 
-    RegExp *regexp = reinterpret_cast<RegExp *>(RegExp::create(ctx->d()->engine, pattern, ignoreCase, multiLine));
+    Scoped<RegExp> regexp(scope, RegExp::create(ctx->d()->engine, pattern, ignoreCase, multiLine));
     if (!regexp->isValid())
         return ctx->throwSyntaxError(QStringLiteral("Invalid regular expression"));