userWidget: Always set actor size inside update()

We also want to ensure the Avatar StBin is sized correctly when an icon
child is used, so always set the actor size inside the `update()`
function.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/1018

js/ui/userWidget.js

@@ -83,13 +83,13 @@ class Avatar extends St.Bin {
                 iconFile = null;
         }
 
-        if (iconFile) {
-            this.child = null;
-
         let { scaleFactor } = St.ThemeContext.get_for_stage(global.stage);
         this.set_size(
             this._iconSize * scaleFactor,
             this._iconSize * scaleFactor);
+
+        if (iconFile) {
+            this.child = null;
             this.style = `
                 background-image: url("${iconFile}");
                 background-size: cover;`;