Don't deadlock on AudioRecord start when reads return 0

When calling start() on an AudioRecord with a HAL that
 returns 0 on a read() operation, the start blocking
 condition was never unblocked.
Add a boolean to track the first read operation so the returned
 number of bytes (mBytesRead) is only evaluated after that
 first read.

Change-Id: I8c735a00d48cd6a0da467ccdf75d3616b38f6afa