Fix preventing from heap overwrite in capture command

There was heap usage error in case of stop of audio framework while
capturePoint was negative. Pointer to reply data was moved but
final silence write was done using original buffer size.
Now silence set is done at the beginning under the condition
that framework has stopped.

Change-Id: I7dab1e922f1813e5fbfd4a64c8b0d15d9465520c