[HIGH] CVE-2019-18888: Prevent argument injection in a MimeTypeGuesser

PKSA-7y15-t1fp-w94f CVE-2019-18888 GHSA-xhh6-956q-4q69

Affected package: symfony/mime

Affected version: >=4.3.0,<4.3.8

Reported by:
GitHub, FriendsOfPHP/security-advisories