UI: Fix Previous icon in System

UI/data/themes/System.qss

@@ -341,7 +341,7 @@ QSlider::handle:horizontal[themeID="tBarSlider"] {
 }
 
 * [themeID="previousIcon"] {
-    qproperty-icon: url(./Dark/media/media_previous.svg);
+    qproperty-icon: url(:/res/images/media/media_previous.svg);
 }
 
 /* YouTube Integration */