Ticket #4717: mcedit: fix segfault at open Syntax file.

How to reproduce:
Start mcedit and go to Options -> Syntax file.

Actual behavior:
Segfault.

  * (file_error): pass second file name as an empty string intead of
    NULL to files_error() to avoid NULL dereference in str_utf8_trunc(),
    str_8bit_trunc(), and str_ascii_trunc().

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>

Author: aborodin

src/filemanager/file.c

@@ -3731,7 +3731,7 @@ panel_operate (void *source_panel, FileOperation operation, gboolean force_singl
 FileProgressStatus
 file_error (file_op_context_t *ctx, gboolean allow_retry, const char *format, const char *file)
 {
-    return files_error (ctx, allow_retry, format, file, NULL);
+    return files_error (ctx, allow_retry, format, file, "");
 }
 
 /* --------------------------------------------------------------------------------------------- */