Removed a couple of deadlocks caused by missing DisplayDriver unlocks

remove possible NULL pointer crash in LayerData
Added low-level clipping to ViewDriver
Some minor UI tweaks to WinBorder


git-svn-id: file:///srv/svn/repos/haiku/trunk/current@10216 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/servers/app/server/ViewDriver.cpp

@@ -753,6 +753,7 @@ void ViewDriver::SetDrawData(const DrawData *d, bool set_font_data)
 		unlock=true;
 	}
 	
+	drawview->ConstrainClippingRegion(d->clipReg);
 	drawview->SetPenSize(d->pensize);
 	drawview->SetDrawingMode(d->draw_mode);
 	drawview->SetHighColor(d->highcolor.GetColor32());