use custom mpv config folder

not the first time the default location has caused problems for users
https://anki.tenderapp.com/discussions/ankidesktop/29531-bug-ankis-version-of-mpv-loads-mpvconf-from-configmpv-on-macos

anki/sound.py

@@ -88,6 +88,10 @@ from anki.mpv import MPV, MPVBase
 
 mpvPath, mpvEnv = _packagedCmd(["mpv"])
 
+def setMpvConfigBase(base):
+    global mpvEnv
+    mpvEnv['XDG_CONFIG_HOME'] = base
+
 class MpvManager(MPV):
 
     executable = mpvPath[0]

aqt/profiles.py

@@ -22,6 +22,7 @@ from aqt.utils import showWarning
 from aqt import appHelpSite
 import aqt.forms
 from send2trash import send2trash
+import anki.sound
 
 metaConf = dict(
     ver=0,
@@ -67,6 +68,8 @@ class ProfileManager:
         # instantiate base folder
         self._setBaseFolder(base)
 
+        anki.sound.setMpvConfigBase(self.base)
+
     def setupMeta(self):
         # load metadata
         self.firstRun = self._loadMeta()