x11: slightly safer X11 error handler behavior

The X11 error handler is global, and not per-display. If another Xlib
user exists in the process, they can conflict. In theory, it might
happen that e.g. another library sets an error handler (overwriting the
mpv one), and some time after mpv closes its display, restores the error
handler to mpv's one. To mitigate this, check if the error log instance
is actually set, instead of possibly crashing.

The change in vo_x11_uninit() is mostly cosmetic.

1 files changed, 4 insertions, 1 deletions

diff --git a/video/out/x11_common.c b/video/out/x11_common.c
index 009f7e4bf6..656509edca 100644
--- a/video/out/x11_common.c
+++ b/video/out/x11_common.c
@@ -280,6 +280,9 @@ static void vo_set_cursor_hidden(struct vo *vo, bool cursor_hidden)
 static int x11_errorhandler(Display *display, XErrorEvent *event)
 {
     struct mp_log *log = x11_error_output;
+    if (!log)
+        return 0;
+
     char msg[60];
     XGetErrorText(display, event->error_code, (char *) &msg, sizeof(msg));
 
@@ -746,8 +749,8 @@ void vo_x11_uninit(struct vo *vo)
     if (x11->xim)
         XCloseIM(x11->xim);
     if (x11->display) {
-        x11_error_output = NULL;
         XSetErrorHandler(NULL);
+        x11_error_output = NULL;
         XCloseDisplay(x11->display);
     }