[gnome-shell] screenshot: Return error when stream creation fails

[Carlos Garnacho <carlosg src gnome org>]

commit eb51942a051f18f5993914968fcefb00a56c3625
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Mar 24 07:44:31 2020 +0100

    screenshot: Return error when stream creation fails
    
    The Shell.Screenshot API expects valid output streams for writing the
    completed screenshot, not NULL.
    
    Handle this properly by returning an error instead of passing it on
    to the screenshot.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1123

 js/ui/screenshot.js | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)
---
diff --git a/js/ui/screenshot.js b/js/ui/screenshot.js
index 09f5c5109f..78afc4ae47 100644
--- a/js/ui/screenshot.js
+++ b/js/ui/screenshot.js
@@ -84,7 +84,7 @@ var ScreenshotService = class {
         }
     }
 
-    _createStream(filename) {
+    _createStream(filename, invocation) {
         if (filename == '')
             return [Gio.MemoryOutputStream.new_resizable(), null];
 
@@ -94,6 +94,7 @@ var ScreenshotService = class {
                 let stream = file.replace(null, false, Gio.FileCreateFlags.NONE, null);
                 return [stream, file];
             } catch (e) {
+                invocation.return_value(GLib.Variant.new('(bs)', [false, '']));
                 return [null, null];
             }
         }
@@ -104,10 +105,11 @@ var ScreenshotService = class {
                 return [stream, file];
             } catch (e) {
                 if (!e.matches(Gio.IOErrorEnum, Gio.IOErrorEnum.EXISTS))
-                    return [null, null];
+                    break;
             }
         }
 
+        invocation.return_value(GLib.Variant.new('(bs)', [false, '']));
         return [null, null];
     }
 
@@ -169,7 +171,9 @@ var ScreenshotService = class {
         if (!screenshot)
             return;
 
-        let [stream, file] = this._createStream(filename);
+        let [stream, file] = this._createStream(filename, invocation);
+        if (!stream)
+            return;
 
         screenshot.screenshot_area(x, y, width, height, stream,
             (o, res) => {
@@ -190,7 +194,9 @@ var ScreenshotService = class {
         if (!screenshot)
             return;
 
-        let [stream, file] = this._createStream(filename);
+        let [stream, file] = this._createStream(filename, invocation);
+        if (!stream)
+            return;
 
         screenshot.screenshot_window(includeFrame, includeCursor, stream,
             (o, res) => {
@@ -211,7 +217,9 @@ var ScreenshotService = class {
         if (!screenshot)
             return;
 
-        let [stream, file] = this._createStream(filename);
+        let [stream, file] = this._createStream(filename, invocation);
+        if (!stream)
+            return;
 
         screenshot.screenshot(includeCursor, stream,
             (o, res) => {