Make ValueValidate() of the ContactsWD field type actually check the value

The values of ContactsWD dynamic fields are integers greater zero, specifically the keys of ContactsWithData in the dynamic field config. But ValueValidate() does not check for that.

I filed that for rel-11_0 as no actual bad effects are known.

---
ContactsWithData:
  '1':
    Age: '
    Call sign: DL2RDS
    Name: bernhard
    ValidID: '1'
  '2':
    Age: '18'
    Call sign: DL7KUH
    Name: muh
    ValidID: '1'
MandatoryFields: Call sign
MandatoryFieldsComputed:
- Name
- ValidID
- Call sign
PossibleValues:
  Age: Alter
  Call sign: Rufzeichen
  Name: Name
  ValidID: Valid ID Feld 1
SearchableFields: ''
SearchableFieldsComputed:
- Name
SortOrder: Name,Age,Call sign
SortOrderComputed:
- Name
- Age
- Call sign
- ValidID
Tooltip: ''
TranslatableValues: '0'