Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the file
`.reuse/dep5`.
This commit also adds a Github workflow to check pull requests and adapts
copyright.pl to the changes.
Closes#8869
... fixes a memory leak with at least IMAP when remove_handle is never
called and the transfer is abruptly just abandoned early.
Test 1552 added to verify
Detected by OSS-fuzz
Assisted-by: Max Dymond
Closes#1954
