[polari] userList: Fix warning during filtering

[Florian Müllner <fmuellner src gnome org>]

commit c75e8c38d881d35c0ba3f0d2b99f4af9881c010b
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Mar 31 18:59:17 2015 +0200

    userList: Fix warning during filtering
    
    We compute the popover height by adding the heights of n rows from
    the first visible one. However when filtering turns out no match,
    we don't have a visible row to start from - use the row at index 0
    in that case to avoid a warning.

 src/userList.js |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/src/userList.js b/src/userList.js
index d81c3ad..6e03051 100644
--- a/src/userList.js
+++ b/src/userList.js
@@ -420,7 +420,11 @@ const UserList = new Lang.Class({
         this._updateHeightId = Mainloop.idle_add(Lang.bind(this, function() {
             let topRow = this._list.get_row_at_y(this.widget.vadjustment.value);
             let membersShown = Math.min(this.numRows, MAX_USERS_SHOWN);
-            let index = Math.min(topRow.get_index(), this.numRows - membersShown);
+            // topRow is unset when all rows are hidden due to filtering,
+            // base height on the first membersShown rows in that case
+            let index = 0;
+            if (topRow)
+                index = Math.min(topRow.get_index(), this.numRows - membersShown);
             let height = 0;
 
             for (let i = 0; i < membersShown; i++)