patch 8.2.3763: when editing the cmdline a callback may cause a scroll up

Problem:    When editing the command line a FocusLost callback may cause the
            screen to scroll up.
Solution:   Do not redraw at the last line but at the same place where the
            command line was before. (closes #9295)

src/ex_getln.c

@@ -3730,6 +3730,10 @@ redrawcmdline(void)
     redrawcmdline_ex(TRUE);
 }
 
+/*
+ * When "do_compute_cmdrow" is TRUE the command line is redrawn at the bottom.
+ * If FALSE cmdline_row is used, which should redraw in the same place.
+ */
     void
 redrawcmdline_ex(int do_compute_cmdrow)
 {