[BUGFIX] Install Tool: Show titles of failed image tests

"Test image formats" tries to convert different media types
to JPG. If one of these conversions fails, you will get an
error message but no hint about what media type failed to convert.

Change-Id: Ie35c7e3529064c99cb8b3ef7d6eb542142b58a56
Resolves: #53632
Releases: 6.2
Reviewed-on: https://review.typo3.org/25396
Reviewed-by: Stefan Froemken
Tested-by: Stefan Froemken
Reviewed-by: Dan Untenzu
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert