Make profiling of pixmap cache events more consistent

Previously canceled replies weren't reported, the cache count was
reported before it was updated, and the request or implicit sizes
were reported instead of the size actually stored in memory.

Task-number: QTBUG-37890
Change-Id: I9d9d9f6b9bfa75c7d56b778fc8174bda4e842d72
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Support shutting down the render thread without an OpenGL context.

[ChangeLog][QtQuick][SceneGraph] There might not be an OpenGL context
bound when QQuickWindow::sceneGraphInvalidated() is emitted if an
error occurs while cleaning up the scene graph (such as
EGL_CONTEXT_LOST). This is according to the documentation, but has
never occurred in practice before.

Change-Id: I13dbfbb4b6d0d27fa42fcb8b54df16ea02284807
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>