stop music when entering zonk mode if no bgm

vacation.p8

@@ -720,7 +720,11 @@ function zonk_mode:av()
  if (type(self.file) == "string") self.file = split(self.file, "\n")
  if (not self.file) self:nf()
  assert(self.file)
- if (self.bgm and (musicmode & 2 == 0)) music(self.bgm,1000,7)
+ if self.bgm and not self.xbgm and (musicmode & 2 == 0) then
+  music(self.bgm,1000,7)
+ else
+  music(-1, 250)
+ end
 end
 
 function zonk_mode:onmchg()