richedit: Private movement of cursors in text insertion should not cause WM_NOTIFY...

richedit: Private movement of cursors in text insertion should not cause WM_NOTIFY to be sent.

As text is inserted, the cursor is moved to the end, and then back to
offset 0. A reordering of operations prevents a WM_NOTIFY from being
sent on cursor being moved to the end, and another by being moved
back to the beginning. If the cursor was not at offset 0, then
exactly one WM_NOTIFY must be sent, for the movement from previous
position to the beginning.  With tests to prove this change and the
previous one (modify flag should be off on WM_SETTEXT-caused
WM_NOTIFY).