Adwaita: progressbar style fix

Reset styling on the progress node when trough node has the `empty'
styleclass.

See https://bugzilla.gnome.org/show_bug.cgi?id=774695

gtk/theme/Adwaita/_common.scss

@@ -3265,6 +3265,8 @@ progressbar {
       border-radius: 0;
     }
   }
+
+  trough.empty progress { all: unset; } // makes the progress indicator disappear, when the fraction is 0
 }
 
 

gtk/theme/Adwaita/gtk-contained-dark.css

@@ -3699,6 +3699,8 @@ progressbar {
     progressbar.osd progress {
       border-style: none;
       border-radius: 0; }
+  progressbar trough.empty progress {
+    all: unset; }
 
 /*************
  * Level Bar *

gtk/theme/Adwaita/gtk-contained.css

@@ -3730,6 +3730,8 @@ progressbar {
     progressbar.osd progress {
       border-style: none;
       border-radius: 0; }
+  progressbar trough.empty progress {
+    all: unset; }
 
 /*************
  * Level Bar *