Fixed crashes when using QImage in combination with QCoreApplication.

As long as fonts weren't used we supported using QImage in combination
with QCoreApplication in 4.x, and there's no reason we can't continue
doing so.

Task-number: QTBUG-29643
Change-Id: I2cf351d3c93f1c175bbf624e45024d39ab913111
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

src/gui/image/qimage.cpp

@@ -4944,7 +4944,10 @@ QPaintEngine *QImage::paintEngine() const
 
     if (!d->paintEngine) {
         QPaintDevice *paintDevice = const_cast<QImage *>(this);
-        QPaintEngine *paintEngine = QGuiApplicationPrivate::platformIntegration()->createImagePaintEngine(paintDevice);
+        QPaintEngine *paintEngine = 0;
+        QPlatformIntegration *platformIntegration = QGuiApplicationPrivate::platformIntegration();
+        if (platformIntegration)
+            paintEngine = platformIntegration->createImagePaintEngine(paintDevice);
         d->paintEngine = paintEngine ? paintEngine : new QRasterPaintEngine(paintDevice);
     }
 

src/gui/text/qfont.cpp

@@ -672,7 +672,7 @@ void QFontPrivate::detachButKeepEngineData(QFont *font)
     \sa QGuiApplication::setFont(), QGuiApplication::font()
 */
 QFont::QFont()
-    : d(QGuiApplication::font().d.data()), resolve_mask(0)
+    : d(QGuiApplicationPrivate::instance() ? QGuiApplication::font().d.data() : new QFontPrivate()), resolve_mask(0)
 {
 }
 

tests/auto/gui/image/qimage/tst_qimage.cpp

@@ -2115,5 +2115,5 @@ void tst_QImage::cleanupFunctions()
 
 }
 
-QTEST_MAIN(tst_QImage)
+QTEST_GUILESS_MAIN(tst_QImage)
 #include "tst_qimage.moc"