[gnome-shell] extensionSystem: Don't load an extension with invalid stylesheet

[Marco Trevisan <marcotrevi src gnome org>]

commit 5b3ff7184eab6c128528a7cdc7b42b2636a6d022
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Fri Aug 3 17:46:27 2018 +0200

    extensionSystem: Don't load an extension with invalid stylesheet
    
    We currently assign the stylesheet to an extension whenever the file exists,
    regardless of whether it actually loaded successfully or not.
    And thus we load an extension that ships a stylesheet even if that file can't
    be used.
    
    There is no point in trying to load an extension if its stylesheet wasn't
    loaded in the first place, so make sure this happens only on success.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/188

 js/ui/extensionSystem.js | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
---
diff --git a/js/ui/extensionSystem.js b/js/ui/extensionSystem.js
index e35c01ab8..3f23d273e 100644
--- a/js/ui/extensionSystem.js
+++ b/js/ui/extensionSystem.js
@@ -115,13 +115,18 @@ function enableExtension(uuid) {
     extensionOrder.push(uuid);
 
     let stylesheetNames = [global.session_mode + '.css', 'stylesheet.css'];
+    let theme = St.ThemeContext.get_for_stage(global.stage).get_theme();
     for (let i = 0; i < stylesheetNames.length; i++) {
-        let stylesheetFile = extension.dir.get_child(stylesheetNames[i]);
-        if (stylesheetFile.query_exists(null)) {
-            let theme = St.ThemeContext.get_for_stage(global.stage).get_theme();
+        try {
+            let stylesheetFile = extension.dir.get_child(stylesheetNames[i]);
             theme.load_stylesheet(stylesheetFile);
             extension.stylesheet = stylesheetFile;
             break;
+        } catch (e) {
+            if (e.matches(Gio.IOErrorEnum, Gio.IOErrorEnum.NOT_FOUND))
+                continue; // not an error
+            log(`Failed to load stylesheet for extension ${uuid}: ${e.message}`);
+            return;
         }
     }