riched20: Make EM_LINELENGTH work correctly for non-final paragraphs containing exactly one screen line.

Otherwise, an IStream_SetSize call followed by an IStream_Read call 
could fail with STG_E_DOCFILECORRUPT.

It has a tendency to trigger X11 bugs, and it's not really useful anyway.

This lets ddraw dlls built on a machine with OpenGL present run on other 
machines that may not have the OpenGL libraries installed.

anybody had any doubts about what they actually do.