Gui: Fix stylesheet loading order

For some platforms due to event loop and timer triggering being not
deterministic stylesheets could be loaded before style parameters were
fully loaded. This caused warnings about style parameters to appear
potentially confusing users.

This commit changes the stylesheet loading to happen much earlier in the
process so the stylesheet is applied before theme preselection has
chance to happen.

src/Gui/StartupProcess.cpp

@@ -225,6 +225,7 @@ void StartupPostProcess::execute()
     setLocale();
     setCursorFlashing();
     setQtStyle();
+    setStyleSheet();
     checkOpenGL();
     loadOpenInventor();
     setBranding();
@@ -503,8 +504,6 @@ void StartupPostProcess::activateWorkbench()
         fcApp->initSpaceball(mainWindow);
     }
 
-    setStyleSheet();
-
     // Now run the background autoload, for workbenches that should be loaded at startup, but not
     // displayed to the user immediately
     autoloadModules(wb);