Xcb

xcb_get_image_reply() NULL Deref on malloc() Failure

The XCB image-reply handler in the screen-streaming bridge allocated a buffer with `malloc()` and immediately wrote to it with `memset()` and `memcpy()` without checking for allocation failure. Under memory pressure, this produces a null-pointer dereference that crashes the process, turning a resource-exhaustion condition into an immediate denial of service. The fix adds a NULL check that frees the intermediate reply and returns early instead of writing to invalid memory.