f_lavfi: don't propagate filter failure if creation fails

Filters that fail to create are not supposed to do this. Generally it
should happen in process() only.

This fixes the previous commit. If a filter could not be created, it
"trashed" the wrapper filter with the failure. (Even if the wrapper were
to handle were to handle failures of sub-filter, it couldn't handle init
failure because it cannot call mp_filter_set_error_handler() before the
newly created filter is actually returned.)

Fixes: #7465 (attempt 2)

0 files changed, 0 insertions, 0 deletions