Fix music not automatically playing when using shareware iwad.

musinfo is not tested or parsed for shareware iwads, but the musinfo list was not set appropriately.

prboom2/src/p_setup.c

@@ -3681,6 +3681,10 @@ void P_SetupLevel(int episode, int map, int playermask, int skill)
  {
  S_ParseMusInfo(lumpname);
  }
+ else
+ {
+ musinfo.items[0] = -1;
+ }
 
  // Make sure all sounds are stopped before Z_FreeTag.
  S_Start();