[BUGFIX] Highlight validation errors for unbound Form ViewHelpers (Revision 4)

This change makes sure that the error class attribute is set on
validation/property-mapping errors even if the "property" argument
is not specified on the respective Form ViewHelper.

Change-Id: I18c99dcd057435a15ebdf2faf55c7cbfc83cb47f
Fixes: #47363
Releases: master, 2.0
Revision-Id: 0d5278bc2b1cc566241a21ce1fe36c353d213ca5