Fix crash in pipewiresourcestream.cpp

Tentative fix for common crash: https://crash-reports.kde.org/organizations/kde/issues/5819/?project=9&query=is%3Aunresolved&referrer=issue-stream&stream_index=0

Comparing with https://docs.pipewire.org/video-play-fixate_8c-example.html reneg_format we can see some renegotiate events should be ignored and can be invalid.

This is untested.

cc @apol