patch 8.0.0468: after aborting an Ex command g< does not work

Problem:    After aborting an Ex command g< does not work. (Marcin
            Szamotulski)
Solution:   Postpone clearing scrollback messages to until the command line
            has been entered.  Also fix that the screen isn't redrawn if after
            g< the command line is cancelled.
diff --git a/src/ex_getln.c b/src/ex_getln.c
index e96f5b8..a3cac72 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -258,6 +258,7 @@
 	return NULL;			    /* out of memory */
     ccline.cmdlen = ccline.cmdpos = 0;
     ccline.cmdbuff[0] = NUL;
+    sb_text_start_cmdline();
 
     /* autoindent for :insert and :append */
     if (firstc <= 0)
@@ -2083,6 +2084,7 @@
 #ifdef CURSOR_SHAPE
     ui_cursor_shape();		/* may show different cursor shape */
 #endif
+    sb_text_end_cmdline();
 
     {
 	char_u *p = ccline.cmdbuff;