patch 9.1.1193: Unnecessary use of STRCAT() in au_event_disable()

Problem:  Unnecessary use of STRCAT() in au_event_disable().  STRCAT()
          seeks to the end of new_ei, but here the end is already known.
Solution: Use STRCPY() and add p_ei_len to new_ei.  Also fix a typo in a
          comment.  Add a test that 'eventignore' works in :argdo
          (zeertzjq).

closes: #16844

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/ex_getln.c b/src/ex_getln.c
index fa1ea99..bc99674 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -4716,7 +4716,7 @@
     State = MODE_NORMAL;
     setmouse();
 
-    // Reset here so it can be set by a CmdWinEnter autocommand.
+    // Reset here so it can be set by a CmdwinEnter autocommand.
     cmdwin_result = 0;
 
     // Trigger CmdwinEnter autocommands.