vCard v4.0 serialization: LOGO without explicit VALUE=URI

[respiranto]

Version: 4.5.5

This is not a "real" bug, but merely an inconsistency.

When serializing a LOGO (parsed from v3.0, or from v4.0 without explicit VALUE=URI), it does not get an explicit VALUE=URI parameter.
This is not the case when parsing from v4.0 with explicit VALUE=URI.
All of PHOTO, SOUND, and KEY always get an explicit VALUE=URI (when identified as URI, see also #677).