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.

src/gui.c

@@ -630,7 +630,7 @@ gui_init(void)
      * where Vim was started. */
     emsg_on_display = FALSE;
     msg_scrolled = 0;
-    clear_sb_text();
+    clear_sb_text(TRUE);
     need_wait_return = FALSE;
     msg_didany = FALSE;