fix(prefs): cast values to string before binary SQL storage

[TDannhauer]

Summary

• Cast preference values to strings with strval() before storing them as Horde_Db_Value_Binary in horde_prefs
• Fixes checkbox and number preferences (e.g. IMP use_trash) that appeared to save successfully but reloaded with empty values
• Root cause: integer scalars passed to the PDO blob layer were treated as non-strings and persisted as empty binary data

Problem

The preferences UI stores checkbox values via intval(), producing integer 0/1. Horde_Prefs_Storage_Sql passed those values directly to Horde_Db_Value_Binary. The PDO blob helper only serializes string data; integers were written as empty blobs.

Observed symptom in IMP:

1. User enables “Move deleted messages to Trash”
2. Horde shows “Your preferences have been updated.”
3. After reload, the checkbox is unchecked and trash behavior is unchanged
4. Database row exists but pref_value is empty

Solution

Normalize the value to a string before charset conversion and binary wrapping:

$value = strval(Horde_String::convertCharset($value, 'UTF-8', $charset));
$value = new Horde_Db_Value_Binary($value);

Preference storage is string-based by design; this keeps SQL storage aligned with that contract regardless of upstream scalar types.

Test plan

• Save IMP preference use_trash as enabled for a test user
• Confirm horde_prefs.pref_value contains 1 (not an empty blob)
• Reload preferences UI and verify the checkbox stays checked
• Verify trash mailbox selection appears after use_trash is enabled
• Save a checkbox preference as disabled and confirm 0 is stored correctly
• Regression: save a text/textarea preference and confirm unchanged behavior

[ralflang]

I think we should strval before Horde_String - saves a lot of headache.
Also an opportunity to switch to PSR-4 HordeString class.