user32: Pass pConv to WDML_Global2DataHandle so that it can be correcly passed to DdeCreateDataHandle.

Kudos to Daniel Remenak for his help.

Certain operations will simply not be done for windowless richedit
controls, such as WM_PAINT which isn't done for windowless richedit
controls since ITextServices provides a TxDraw method.

The methods in ITextHost are mostly thin wrappers around functions that
take a handle to a window as their first parameter.  This patch just
uses the wrapper functions provided by ITextHost instead of using the
functions that require a handle to a window that the editor might now
have (for windowless richedit controls).