fixed some issues with the software renderer when surfaces are made current.

there was several issues:
- when a surface was made non-current, the last frame wasn't shown and the buffer could stay locked
- when a surface was made current the 2nd time, it would not dequeue a new buffer

now, queue/dequeue are done when the surface is made current.

for this to work, a new query() hook had to be added on android_native_window_t, it allows to retrieve some attributes of a window (currently only width and height).