The call to GetClientRect returns 0 values for the returned RECT when
called in WM_NCCREATE in on Windows, which ended up causing an assertion
error when Wine's riched20.dll replaces the native version. Moving the
call to WM_CREATE fixes this problem (probably because NCCALCSIZE is
called in between).

There was a missing call to ShowCaret after the caret was created.

The function ME_FindRunInRow uses two parameters to return values by
reference, and treated these parameters as if they were optional except
for the start of the function which set *pbCaretAtEnd without checking
to see if was a NULL pointer.

Previous version (commit 3bacdaf6) was totally incorrect.
Thanks to Paul Vriens for pointing this out.