xcbgrab: Do not assume the non shm image data is always available

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavdevice/xcbgrab.c

@@ -145,13 +145,25 @@ static int xcbgrab_frame(AVFormatContext *s, AVPacket *pkt)
     xcb_get_image_cookie_t iq;
     xcb_get_image_reply_t *img;
     xcb_drawable_t drawable = c->screen->root;
+    xcb_generic_error_t *e = NULL;
     uint8_t *data;
     int length, ret;
 
     iq  = xcb_get_image(c->conn, XCB_IMAGE_FORMAT_Z_PIXMAP, drawable,
                         c->x, c->y, c->width, c->height, ~0);
 
-    img = xcb_get_image_reply(c->conn, iq, NULL);
+    img = xcb_get_image_reply(c->conn, iq, &e);
+
+    if (e) {
+        av_log(s, AV_LOG_ERROR,
+               "Cannot get the image data "
+               "event_error: response_type:%u error_code:%u "
+               "sequence:%u resource_id:%u minor_code:%u major_code:%u.\n",
+               e->response_type, e->error_code,
+               e->sequence, e->resource_id, e->minor_code, e->major_code);
+        return AVERROR(EACCES);
+    }
+
     if (!img)
         return AVERROR(EAGAIN);
 
@@ -405,7 +417,7 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
         ret = xcbgrab_frame(s, pkt);
 
 #if CONFIG_LIBXCB_XFIXES
-    if (c->draw_mouse && p->same_screen)
+    if (ret >= 0 && c->draw_mouse && p->same_screen)
         xcbgrab_draw_mouse(s, pkt, p, geo);
 #endif