vim-patch:9.0.0099: scrollback can be wrong after redrawing the command line (#19562)

Problem:    Scrollback can be wrong after redrawing the command line.
Solution:   Clear unfinished scrollback when redrawing. (closes vim/vim#10807)
46af7bc08d

src/nvim/ex_getln.c

@@ -3823,6 +3823,7 @@ void redrawcmd(void)
 
   redrawing_cmdline = true;
 
+  sb_text_restart_cmdline();
   msg_start();
   redrawcmdprompt();