filepush: do not send evtEOF when playback is stopping

While playback is within the last m_buffersize of the file,
the filepush thread will poll the decoder, to detect
when it is empty.
As soon as it is, an evtEOF event will be sent.
For a timeshift, this situation can last for a long time,
because the file will grow with the same rate as the playback
point proceeds.
Now when a seek (skip) is attempted in this situation, the
decoder will be flushed, causing the filepush thread to assume
we have all the required conditions for an EOF event.
However, if an evtEOF event would be sent by the filepush
thread, that would cause the timeshift to switch to the
live point.
Therefore, when the filepush thread is to be stopped, as will
happen for a seek/skip, we should not send an evtEOF event when
the decoder is empty.
Instead, just break out of the thread, and emit an evtStopped.

thanks to betacentauri for pointing out this issue