QTemporaryFile: Return early if the passed in QFile cannot be opened

Change-Id: I97f00163c24f74d31e1b41ec7337f72600bda2d5
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Mikhail Svetkin <mikhail.svetkin@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qtemporaryfile.cpp

@@ -908,8 +908,8 @@ QTemporaryFile *QTemporaryFile::createNativeFile(QFile &file)
         qint64 old_off = 0;
         if(wasOpen)
             old_off = file.pos();
-        else
-            file.open(QIODevice::ReadOnly);
+        else if (!file.open(QIODevice::ReadOnly))
+            return nullptr;
         //dump data
         QTemporaryFile *ret = new QTemporaryFile;
         if (ret->open()) {