iconGrid: Make sure the style is updated before computing the layout

In some cases the style-changed signal hasn't been emitted when
_computeLayout() is called, resulting in the use of the default spacing
and item size values for the calculations.

One case where this happens is when starting a search. Right after the
initialization of GridSearchResults, _computeLayout() is called from
_getMaxDisplayedResults() and the style-changed signal hasn't been
emitted yet. The computed layout will be wrong and the maximum
number of results will also be wrong.

To prevent this from happening, make sure the style has been updated
before doing the calculations in _computeLayout().

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/110

js/ui/iconGrid.js

@@ -602,6 +602,8 @@ var IconGrid = GObject.registerClass({
     }
 
     _computeLayout(forWidth) {
+        this.ensure_style();
+
         let nColumns = 0;
         let usedWidth = this.leftPadding + this.rightPadding;
         let spacing = this._getSpacing();