[BUGFIX] Report migration errors in TceformsUpdateWizard

TceformsUpdateWizard should report errors if a migration
failed due to a missing source file.

Resolves: #57575
Releases: 6.3, 6.2
Change-Id: I68af9a5155f7d6190a22cc4986ef4a467b747737
Reviewed-on: https://review.typo3.org/29100
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Alexander Opitz
Tested-by: Alexander Opitz
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters