SF: Check ViewFrame validity before sending to hwc

Check if ViewFrame is valid before sending to hwc to make sure
composition produces valid values.

A ViewFrame can get invalid values when the framework is disconnected
which is a step necessary for some testing scenarios.

Change-Id: I2ad76061b6664dbb7d2aa3d66acaf99b880aedfe
sf: Clear FrameBuffer only if there are GLES composed layers

Clear FrameBuffer Target only if there are layers to be composed by
GLES. Otherwise, it results unnecessary gl calls and increases power
consumption in full MDP comp use cases.

Change-Id: Ib84c4fe154bb67668e4e8b8ce2f2328c55aed7c6
Merge pull request #4 from LiquidSmooth/kitkat

marge last Liquid pull request