Ensure we have a valid context before drawing keyframes

src/timeline2/view/qml/KeyframeView.qml

@@ -266,8 +266,9 @@ Rectangle
             if (kfrCount < 2) {
                 return
             }
-            context.beginPath()
-            context.fillStyle = Qt.rgba(0,0,0.8, 0.5);
+            var ctx = getContext("2d");
+            ctx.beginPath()
+            ctx.fillStyle = Qt.rgba(0,0,0.8, 0.5);
             paths = []
             var xpos
             var ypos
@@ -291,10 +292,10 @@ Rectangle
             paths.push(compline.createObject(keyframecanvas, {"x": parent.width, "y": ypos} ))
             paths.push(compline.createObject(keyframecanvas, {"x": parent.width, "y": parent.height} ))
             myPath.pathElements = paths
-            context.clearRect(0,0, width, height);
-            context.path = myPath;
-            context.closePath()
-            context.fill()
+            ctx.clearRect(0,0, width, height);
+            ctx.path = myPath;
+            ctx.closePath()
+            ctx.fill()
         }
     }
 }