decoder/Control: remove attribute client_is_waiting

This optimization is useless because sane pthread_cond_signal()
implementations check the number of waiters and do not invoke a system
call if there are none.

src/decoder/Bridge.cxx

@@ -145,8 +145,7 @@ DecoderBridge::FlushChunk() noexcept
 		dc.pipe->Push(std::move(chunk));
 
 	const std::lock_guard<Mutex> protect(dc.mutex);
-	if (dc.client_is_waiting)
-		dc.client_cond.notify_one();
+	dc.client_cond.notify_one();
 }
 
 bool

src/decoder/Control.cxx

@@ -43,13 +43,7 @@ DecoderControl::~DecoderControl() noexcept
 void
 DecoderControl::WaitForDecoder(std::unique_lock<Mutex> &lock) noexcept
 {
-	assert(!client_is_waiting);
-	client_is_waiting = true;
-
 	client_cond.wait(lock);
-
-	assert(client_is_waiting);
-	client_is_waiting = false;
 }
 
 void

src/decoder/Control.hxx

@@ -111,13 +111,6 @@ private:
 	bool quit;
 
 public:
-	/**
-	 * Is the client currently waiting for the DecoderThread?  If
-	 * false, the DecoderThread may omit invoking Cond::signal(),
-	 * reducing the number of system calls.
-	 */
-	bool client_is_waiting = false;
-
 	bool seek_error;
 	bool seekable;
 	SongTime seek_time;