patch 8.1.2250: CTRL-U and CTRL-D don't work in popup window

Problem:    CTRL-U and CTRL-D don't work in popup window.
Solution:   Initialize 'scroll'.  Add "lastline" in popup_getpos().
            (closes #5170)
diff --git a/src/popupwin.c b/src/popupwin.c
index d6e6207..ddb1254 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -1373,6 +1373,8 @@
 	wp->w_height = wp->w_maxheight;
     if (wp->w_height > Rows - wp->w_winrow)
 	wp->w_height = Rows - wp->w_winrow;
+    if (wp->w_height != org_height)
+	win_comp_scroll(wp);
 
     if (center_vert)
     {
@@ -2500,6 +2502,7 @@
 
 	dict_add_number(dict, "scrollbar", wp->w_has_scrollbar);
 	dict_add_number(dict, "firstline", wp->w_topline);
+	dict_add_number(dict, "lastline", wp->w_botline - 1);
 	dict_add_number(dict, "visible",
 		      win_valid(wp) && (wp->w_popup_flags & POPF_HIDDEN) == 0);