glTF: More rendering related error handling

If any error occurs related to glTF rendering, a question
mark is displayed at the place of the OpenGL window
(Question mark is a general concept of media objects).

Change-Id: Id7df5a47a4dd6832e640b3a7cb3c7712ebfb4408

avmedia/source/opengl/oglframegrabber.cxx

@@ -38,7 +38,12 @@ uno::Reference< css::graphic::XGraphic > SAL_CALL OGLFrameGrabber::grabFrame( do
 {
     boost::scoped_array<sal_uInt8> pBuffer(new sal_uInt8[m_rHandle.viewport.width * m_rHandle.viewport.height * 4]);
     glTFHandle* pHandle = &m_rHandle;
-    gltf_renderer_get_bitmap(&pHandle, 1, (char*)pBuffer.get(), GL_BGRA);
+    int nRet = gltf_renderer_get_bitmap(&pHandle, 1, (char*)pBuffer.get(), GL_BGRA);
+    if( nRet != 0 )
+    {
+        SAL_WARN("avmedia.opengl", "Error occured while rendering to bitmap! Error code: " << nRet);
+        return uno::Reference< css::graphic::XGraphic >();
+    }
     BitmapEx aBitmap = OpenGLHelper::ConvertBGRABufferToBitmapEx(pBuffer.get(), m_rHandle.viewport.width, m_rHandle.viewport.height);
     return Graphic( aBitmap ).GetXGraphic();
 }

avmedia/source/opengl/oglwindow.cxx

@@ -33,7 +33,12 @@ OGLWindow::~OGLWindow()
 void SAL_CALL OGLWindow::update() throw (css::uno::RuntimeException, std::exception)
 {
     m_rContext.makeCurrent();
-    gltf_prepare_renderer(&m_rHandle);
+    int nRet = gltf_prepare_renderer(&m_rHandle);
+    if( nRet != 0 )
+    {
+        SAL_WARN("avmedia.opengl", "Error occured while preparing for rendering! Error code: " << nRet);
+        return;
+    }
     gltf_renderer(&m_rHandle);
     gltf_complete_renderer(&m_rHandle);
     m_rContext.swapBuffers();