sleep when waiting for cross-fade chunks

When there are not enough decode cross-fade chunks in the buffer yet,
the current code does busy-wait, which will delay the decoder even
more.  sleep instead, expecting the decoder to wake us up.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7272 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/decode.c

@@ -536,10 +536,12 @@ static void decodeParent(PlayerControl * pc, DecoderControl * dc, OutputBuffer *
 						   running, abort
 						   cross fading */
 						doCrossFade = -1;
-					} else
+					} else {
 						/* wait for the
 						   decoder */
+						player_sleep();
 						continue;
+					}
 				}
 			}