canEditProperty() was returning true (editable) when an LDAP attribute
was configured for a field, and false when no attribute was configured.
This is inverted: a field with an LDAP attribute mapping is owned by
LDAP and should not be user-editable, while a field with no mapping is
not sourced from LDAP and the user should be free to set it themselves.
Fixes profile fields being uneditable for all LDAP users whose admin
has not configured attribute mappings for those fields.
Assisted-by: ClaudeCode:claude-sonnet-4-6
Signed-off-by: Anna Larch <anna@nextcloud.com>