StagefrightRecorder: correct the flow of resuming or stopping from pause

1. resume from pause: start the writer first, to avoid frames dropped by
writer due to writer is not started, which caused mosaic frames.

2. stop from pause:  don't start writer, just start encoders and sources,
to avoid unwanted frames are written into clips when stopping in
paused state.

3. recover the pause(dropping frames) in MPEG4Writer.

Change-Id: I4f8f275bce6ac7bc3d4f31f372cc86b362b6c587
CRs-Fixed: 695750 695745
(cherry picked from commit 6061cc0a)