DetachedSong: compare start_time and end_time in IsSame()

This method is used by DecoderControl::IsCurrentSong(), which is used
by the player thread to check whether the current decoder instance can
be reused to seek.  When switching to another song in the same CUE
sheet, previously DetachedSong::IsSame() returned true, and thus the
old decoder instance was used for the new song, not considering the
new end_time.  This led to the old decoder quickly quitting.

src/DetachedSong.hxx

@@ -146,7 +146,9 @@ public:
 	 */
 	gcc_pure
 	bool IsSame(const DetachedSong &other) const {
-		return uri == other.uri;
+		return uri == other.uri &&
+			start_time == other.start_time &&
+			end_time == other.end_time;
 	}
 
 	gcc_pure gcc_nonnull_all