libsaria: Go to new current iterator when picking next

The new "cur" iterator points to a valid song, so I might as well scroll
close to it.

Signed-off-by: Bryan Schumaker <bjschuma@gmail.com>

libsaria/playlist/next.cpp

@@ -31,8 +31,10 @@ namespace libsaria
 
 		remove_track_it(cur, index);
 		schedule_save();
-		if (cur == plist.end())
-			cur = plist.begin();
+		if (index != 0)
+			index--;
+		if (get_size() != 0)
+			RENDER(goto_index(index));
 
 		return res;
 	}