patch 8.1.1999: calling both PlaySoundW() and PlaySoundA()

Problem:    Calling both PlaySoundW() and PlaySoundA().
Solution:   Only use PlaySoundW(). (Dan Thompson, closes #4903)
diff --git a/src/sound.c b/src/sound.c
index 11170af..c3052fd 100644
--- a/src/sound.c
+++ b/src/sound.c
@@ -435,7 +435,7 @@
     void
 f_sound_clear(typval_T *argvars UNUSED, typval_T *rettv UNUSED)
 {
-    PlaySound(NULL, NULL, 0);
+    PlaySoundW(NULL, NULL, 0);
     mciSendString("close all", NULL, 0, NULL);
 }