path_utils: Strip trailing path separators

Path may well end with a '/', e.g. URLs. So strip them away since
otherwise mp_basename finds the wrong part of the given path. In case of
the 'filename' property this simply results in it being set to the whole
URL. But in case of the %f/%F screenshot-template specifiers it may
result in a broken screenshot path, if %f occurs before the first '/'.

Author: WhitePeter

misc/path_utils.c

@@ -43,6 +43,9 @@ char *mp_basename(const char *path)
 {
     char *s;
 
+    /* otherwise the check below finds the wrong index */
+    mp_path_strip_trailing_separator((char *)path);
+
 #if HAVE_DOS_PATHS
     if (!mp_is_url(bstr0(path))) {
         s = strrchr(path, '\\');