{decoder,player}_control: removed duplicate wakeups

Don't wake up the target thread in every iteration of the wait() loop.
Waking it up once, right after the command has been set, must be
enough.

src/player_control.c

@@ -72,10 +72,8 @@ pc_song_deleted(const struct song *song)
 static void
 player_command_wait_locked(void)
 {
-	while (pc.command != PLAYER_COMMAND_NONE) {
-		player_signal();
+	while (pc.command != PLAYER_COMMAND_NONE)
 		g_cond_wait(main_cond, pc.mutex);
-	}
 }
 
 static void
@@ -84,6 +82,7 @@ player_command_locked(enum player_command cmd)
 	assert(pc.command == PLAYER_COMMAND_NONE);
 
 	pc.command = cmd;
+	player_signal();
 	player_command_wait_locked();
 }