[BUGFIX] Fix DB error handling in FrontendUserImageUpdateWizard

The errorCode() method returns a string representation of the error that happened.
Comparing this to an integer value to determine is not reliable. In addition Doctrine
throws Exceptions when database statements fail so this part of the code could not be
reached.
Catch the DBALException, extract the error message and let the re-raised extension
bubble up to show the actual error message to the user.

Change-Id: I042b94329e3d52f9520ded812247ee78a73ea402
Resolves: #79870
Releases: master, 8.7
Reviewed-on: https://review.typo3.org/53130


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>