QQuickSpriteEngine do not use OpenGL without checking for GLContext

In the case that QQuickSpriteEngine::assembledImage() is called when
there is no current OpenGL context, return a null QImage instead of
crashing.  This is needed for the Qt Quick 2d Renderer case.

Change-Id: I75b9b1f31f05cc0800293435d660e498fecc4d20
Reviewed-by: aavit <eirik.aavitsland@digia.com>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>
QQuickCustomParticle: Check for current OpenGL Context before use

QQuickCustomParticle::buildCustomNodes() assumes there is a valid OpenGL
context, but when there is not it will simply crash.  Instead we check
for a valid current OpenGL context first, and return 0 if it is not
availalbe.  This needed for the Qt Quick 2d Renderer.

Change-Id: I6bfcfc8fa9581bfd27015f719fc527c36492eade
Reviewed-by: aavit <eirik.aavitsland@digia.com>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>
Fix a bug in implementation of Accessible.ignored

m_ignored is not really used.

(cherry-picked from dev branch: 2c42d6af19f57ae013da0a4c45b6e1de8fb99e99)
Change-Id: Ic2926fbdf22a6a5bc82fe9f4475b7b8058eacae5
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@theqtcompany.com>
Check list property before component when validating bindings

There are lists that won't accept a component as element. For example
QQuickItem's children will only accept QQuickItems.

Task-number: QTBUG-41848
Change-Id: I0fc7b0d1a4770d596caf681be92dff216f48d32b
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>