[Techdraw] Fix minor bug changing Image Crop...

... from True to False does not fill image view box only approx three quarters.
This was found testing reported issue https://forum.freecadweb.org/viewtopic.php?f=35&t=57537 (otherwise it works as @WandererFan expected)

src/Mod/TechDraw/Gui/QGIViewImage.cpp

@@ -135,7 +135,7 @@ void QGIViewImage::draw()
     }
     m_cliparea->centerAt(0.0,0.0);
 
-    QGIView::draw();
+    drawImage();
 }
 
 void QGIViewImage::drawImage()