libstagefright: fix drainInputBuffers for FlushCompleteEmulation Quirk

Codecs which use the "requires-flush-complete-emulation" require
flushing (draining) the buffers before filling them. The change
"accelerate camera recording start up speed" has changed the order
of filling and draining the buffers which doesn't work well with
the FlushCompleteEmulation quirk

Change-Id: I78193f0aca4a85455393a4cf20d33b919ea6a57e