Canvas: don't crash when getContext("2d") is called on destruction.

We'd assume that a Window existed when that's not always the case.
For example:

import QtQuick 2.4
import QtQuick.Window 2.2
Window {
    Loader {
        sourceComponent: Canvas {
            Component.onDestruction: getContext("2d")
        }
        Component.onCompleted: active = false
    }
}

Change-Id: I5f30876e21ced5658adfa3bac494fd4196e0a7e3
Task-number: QTBUG-42222
Reviewed-by: Ulf Hermann <ulf.hermann@theqtcompany.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/tests/auto/quick/qquickcanvasitem/data/CanvasTestCase.qml b/tests/auto/quick/qquickcanvasitem/data/CanvasTestCase.qml
index b0cae69fe3..e49f0ac462 100644
--- a/tests/auto/quick/qquickcanvasitem/data/CanvasTestCase.qml
+++ b/tests/auto/quick/qquickcanvasitem/data/CanvasTestCase.qml
@@ -25,6 +25,11 @@ TestCase {
      return [];
   }
 
+  function renderStrategyToString(renderStrategy) {
+      return renderStrategy === Canvas.Immediate ? "Canvas.Immediate" :
+            (renderStrategy === Canvas.Threaded ? "Canvas.Threaded" : "Canvas.Cooperative");
+  }
+
   function createCanvasObject(data) {
     return component.createObject(testCase, data.properties);
   }