On creating a 2nd wpesrc in a new pipeline in an app that already has a runnig wpesrc, WPE sometimes doesn't return a buffer on request, leading to a crash. This commit fixes the crash, but not the underlying failure - a 2nd wpesrc can still error out instead. Partially fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/issues/1386 Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1568>