Don't die when finding an unknown email

Summary:
Nowadays with phabricator, etc. it's very common to have commits whose author is not a committer and thus not listed in the accounts file.

Instead of die-ing collect all those emails and print them in the summary, the script will just work fine

Subscribers: svuorela, ostroffjh, jriddell, mwolff, dfaure

Differential Revision: https://phabricator.kde.org/D18568