screensaver: move more repeatedly used code to screensaver's code

Origin commit data
------------------
Commit: 7c1058382f
Author: vanhofen <vanhofen@gmx.de>
Date: 2017-11-25 (Sat, 25 Nov 2017)

Origin message was:
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- screensaver: move more repeatedly used code to screensaver's code

src/gui/screensaver.cpp

@@ -324,6 +324,13 @@ void CScreenSaver::paint()
 	}
 }
 
+bool CScreenSaver::canStart()
+{
+	if (g_settings.screensaver_delay && (time(NULL) - idletime > g_settings.screensaver_delay*60))
+		return true;
+	return false;
+}
+
 bool CScreenSaver::isActive()
 {
 	if(thrScreenSaver)