Do not store cached EGL images in GstMemory QData. Instead, use a
per-DmabufUpload GHashTable to store cache entries with a weak
reference to the GstMemory.
This allows two glupload elements on separate tee branches to have
their own EGL image cache. For this pipeline:
gst-launch-1.0 v4l2src ! tee name=t \
t. ! queue ! glupload ! fakesink
t. ! queue ! glupload ! fakesink
this gets rid of the occasional critical error message:
GStreamer-CRITICAL **: 08:26:33.194: gst_mini_object_unref: assertion 'GST_MINI_OBJECT_REFCOUNT_VALUE (mini_object) > 0' failed
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3880>
485c8ef4b5