user32: Remove redundant visibility checks of a maximized MDI child, add an explanation why we do that.

This reverts commit 6fb1869b.

Change HTTP_EncodeBasicAuth to convert the username and password into 
utf8 before base64 encoding.

wininet: HTTP_HttpQueryInfoW deals with bytes, not characters so update the callers that have this wrong assumption.

instead of crashing so that when used with the replace flag it will
delete an existing value.

Fixes a regression found by Lei Zhang.