[BUGFIX] Respect empty allowedMimeTypes for file uploads

[BUGFIX] Respect empty allowedMimeTypes for file uploads

Make it possible to allow all mime types (except php) within file upload
form elements.
Since there are some default mime types configured within the ext:form
standard setup, you have to remove this default mime types within your
form definition (or reconfigure the default values within your custom
ext:form setup).

FileUpload:

properties:
  allowedMimeTypes:
    0: null
    1: null
    2: null
    3: null

ImageUpload:

properties:
  allowedMimeTypes:
    0: null
    1: null
    2: null

Releases: master, 8.7
Resolves: #82670
Change-Id: Ifa07cceb47978b913f36b8607d4df4724ae22eef
Reviewed-on: https://review.typo3.org/55869
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Tobi Kretschmann <tobi@tobishome.de>
Reviewed-by: Steffen Frese <steffenf14@gmail.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>