[gnome-shell] lookingGlass: Throw a clearer error on referencing invalid result index

[Florian Müllner <fmuellner src gnome org>]

commit ba23fd9989778b32cf7b3377d1d82150e49b9ebd
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Mon May 20 23:27:48 2019 +0200

    lookingGlass: Throw a clearer error on referencing invalid result index
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/700

 js/ui/lookingGlass.js | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/js/ui/lookingGlass.js b/js/ui/lookingGlass.js
index a53fd90db7..2c1239cd5f 100644
--- a/js/ui/lookingGlass.js
+++ b/js/ui/lookingGlass.js
@@ -1010,7 +1010,11 @@ var LookingGlass = class LookingGlass {
     }
 
     getResult(idx) {
-        return this._results[idx - this._offset].o;
+        try {
+            return this._results[idx - this._offset].o;
+        } catch (e) {
+            throw new Error(`Unknown result at index ${idx}`);
+        }
     }
 
     toggle() {