In commit f69cf86a61a8109, I added a call to term_update that happens
when we receive WM_VSCROLL / SB_THUMBPOSITION in the subsidiary
message loop that Windows creates during the handling of WM_SYSCOMMAND
/ SC_VSCROLL. The effect was that interactive dragging of the
scrollbar now redraws the window at every step, whereas previously it
didn't.
A user just pointed out that if you click on one of the scrollbar end
buttons and hold it down until it begins emulating key repeat, the
same bug occurs: the window isn't redrawn until you release the mouse
button and the subsidiary message loop ends.
This commit extends the previous fix to cover all of the WM_VSCROLL
subtypes, instead of just SB_THUMBPOSITION and SB_THUMBTRACK. Redraws
while holding down those scrollbar buttons now work again.
(cherry picked from commit 2029aa55c22631bd1c46df0c7ce817770d38d203)
22d7888b33