patch 9.0.0099: scrollback can be wrong after redrawing the command line

Problem:    Scrollback can be wrong after redrawing the command line.
Solution:   Clear unfinished scrollback when redrawing. (closes #10807)
diff --git a/src/ex_getln.c b/src/ex_getln.c
index a5196fc..2a1fe3d 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -3892,6 +3892,7 @@
 	return;
     }
 
+    sb_text_restart_cmdline();
     msg_start();
     redrawcmdprompt();
 
@@ -4106,7 +4107,7 @@
 
 #if defined(FEAT_EVAL) || defined(FEAT_CMDWIN) || defined(PROTO)
 /*
- * Get pointer to the command line info to use. save_ccline() may clear
+ * Get pointer to the command line info to use. save_cmdline() may clear
  * ccline and put the previous value in prev_ccline.
  */
     static cmdline_info_T *