windows support: fix _wstat misusage

I have no idea when or how this broke, but _wstati64() is the function
we want anyway (64 bit filesize). Possibly this was a mingw-w64 bug.
It's unknown why "wstat()" just doesn't work in this case, as it's not
defined by MSDN and could be defined by mingw as it needs.

Author: wm4

osdep/io.c

@@ -87,7 +87,7 @@ void mp_get_converted_argv(int *argc, char ***argv)
 int mp_stat(const char *path, struct stat *buf)
 {
     wchar_t *wpath = mp_from_utf8(NULL, path);
-    int res = _wstat64(wpath, buf);
+    int res = _wstati64(wpath, buf);
     talloc_free(wpath);
     return res;
 }

osdep/io.h

@@ -55,7 +55,7 @@ struct dirent *mp_readdir(DIR *dir);
 int mp_closedir(DIR *dir);
 int mp_mkdir(const char *path, int mode);
 
-// NOTE: Stat is not overridden with mp_stat, because MinGW-w64 defines it as
+// NOTE: stat is not overridden with mp_stat, because MinGW-w64 defines it as
 //       macro.
 
 #define fprintf(...) mp_fprintf(__VA_ARGS__)