wibox.hierarchy: Only count "really visible" widgets

Widgets with width or height zero cannot really be counted as visible,
so do not do so.

Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/wibox/hierarchy.lua

@@ -157,8 +157,8 @@ function hierarchy_update(self, context, widget, width, height, region, matrix_t
 
     -- Update widget counts
     self._widget_counts = {}
-    if widgets_to_count[self._widget] then
-        self._widget_counts[self._widget] = 1
+    if widgets_to_count[widget] and width > 0 and height > 0 then
+        self._widget_counts[widget] = 1
     end
     for _, h in ipairs(self._children) do
         for w, count in pairs(h._widget_counts) do

spec/wibox/hierarchy_spec.lua

@@ -272,7 +272,8 @@ describe("wibox.hierarchy", function()
                 make_child(child, 10, 20, matrix.identity)
             })
             parent = make_widget({
-                make_child(intermediate, 10, 20, matrix.identity)
+                make_child(intermediate, 10, 20, matrix.identity),
+                make_child(child, 0, 20, matrix.identity)
             })
             unrelated = make_widget(nil)