Fix double clicks in eglfs

The window can be null in the qpa event. This is indicated by the nullWindow
field to be able to differentiate between a dead window and a genuinely
null input.

[ChangeLog] Double click events are now sent correctly on eglfs.

Task-number: QTBUG-40146
Change-Id: I63c8d08e0dec217b929161d2e827e0c273b4dd3e
Reviewed-by: Will Wagner <willw@carallon.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Propagate swapInterval to QGLFormat

Task-number: QTBUG-39370
Change-Id: Ib3a46a0ae24e5f6d690625b1d91be9e599bbc927
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>