Call startPreview after stopping for mUseStillCameraForTimeLapse=true case.

In the case when stop is pressed after takePicture has been called
but the CAMERA_MSG_COMPRESSED_IMAGE message from camera has not yet
been received, preview was not getting restarted. The reason was that
CameraSource::stop sets the camera listener to NULL and hence the
dataCallback() function which handles the CAMERA_MSG_COMPRESSED_IMAGE
message and restarts preview never got called.

Change-Id: Ib8f3bb77d9eab1ed5a67798569025ea0d63d7fd4