typefind: Add new gst_type_find_helper_get_range_full() that returns flow return

And make use of it in the typefind element. It's useful to distinguish
between the different errors why typefinding can fail, and especially to
not consider GST_FLOW_FLUSHING as an actual error.

https://bugzilla.gnome.org/show_bug.cgi?id=796894
4 files changed