Force a repaint of the splash screen.

Ensures the image is painted promptly and does not wait for the event loop
to start. If the ApplicationWindow constructor takes too long then
the event loop paint events don't start and the image only gets painted
at the end.
Refs #10741

Code/Mantid/MantidPlot/src/main.cpp

@@ -200,6 +200,9 @@ int main( int argc, char ** argv )
     const QString versionInfo(Mantid::Kernel::MantidVersion::version());
     splash.showMessage("Release: " + releaseDateTime + " (Version " + versionInfo + ")", Qt::AlignLeft | Qt::AlignBottom);
     splash.show();
+    // If we take too long to get to the event loop then box starts out gray so ensure
+    // it is painted before doing any heavy lifting like the ApplicationWindow init
+    splash.repaint();
     app.processEvents();
 
     bool factorySettings = false;