Wrong charset used in creating search terms when server supports UTF8

**Describe the bug**
Function `int[] search(String msgSequence, SearchTerm term) throws ProtocolException, SearchException` on line 2479 in `IMAPProtocol` class checks if server support UTF8.
In function `private int[] issueSearch(String msgSequence, SearchTerm term, String charset) throws ProtocolException, SearchException, IOException` on line 2532 `Argument` object is created with charset as null.

When null is passed to `SearchSequence#generateSequence()` it defaults to all ASCII text while parsing strings in seach terms.

I don't know if reproduction is needed here.