Queue: "setprio" re-enqueues old song if priority has been raised

This commit changes a minor queue priority design to something which
makes a little bit more sense.

Previously, a song that had already been played would only be
re-enqueued if its priority had just been raised above the current
song's.  This means that if it was already above, it was not
re-enqueued.  That is a surprising behavior, because users expect a
song to be played when its priority is raised.

Now the song is always re-enqueued if its priority is raised (and
above the current song's - no matter if it has already been above
before).

 https://bugs.musicpd.org/view.php?id=4592

NEWS

@@ -1,4 +1,6 @@
 ver 0.19.20 (not yet released)
+* protocol
+  - "setprio" re-enqueues old song if priority has been raised
 * decoder
   - ffmpeg: ignore empty packets
   - pcm: fix corruption bug with partial frames (after short read)

src/queue/Queue.cxx

@@ -426,14 +426,15 @@ Queue::SetPriority(unsigned position, uint8_t priority, int after_order)
 
 		if (_order < (unsigned)after_order) {
 			/* the specified song has been played already
-			   - enqueue it only if its priority has just
-			   become bigger than the current one's */
+			   - enqueue it only if its priority has been
+			   increased and is now bigger than the
+			   current one's */
 
 			const unsigned after_position =
 				OrderToPosition(after_order);
 			const Item *after_item =
 				&items[after_position];
-			if (old_priority > after_item->priority ||
+			if (priority <= old_priority ||
 			    priority <= after_item->priority)
 				/* priority hasn't become bigger */
 				return true;