sink, source: Don't finish move if unlink happens after pa_*_move_all_start()

sink, source: Don't finish move if unlink happens after pa_*_move_all_start()

When a sink input was unlinked between the calls to pa_sink_move_all_start() and
pa_sink_move_all_finish(), pa_sink_move_all_finish() tried to finish the move
of the already unlinked sink input, which lead to an assertion in
pa_sink_input_finish_move(). The same applies for the source side.

This patch fixes the problem by checking the state of the sink input or
source output in pa_*_move_all_finish().

Bug report: https://bugs.freedesktop.org/show_bug.cgi?id=103752