encode \ in xspf location uri also (rfc 3986 has set of characters

that can be in url without encoding, \ doesnt seem to be one of them)

relates to ticket #2218

modules/misc/playlist/xspf.c

@@ -346,6 +346,7 @@ static char *assertUTF8URI( char *psz_name )
             *psz_s == ' ' ||
             *psz_s == '+' ||
             *psz_s == '%' ||
+            *psz_s == '\\' ||
             ( b_uri_is_file && (
             *psz_s == ':' ||
             *psz_s == '"' ||