patch 8.0.1356: using simalt in a GUIEnter autocommand inserts characters

Problem:    Using simalt in a GUIEnter autocommand inserts strange characters.
            (Chih-Long Chang)
Solution:   Ignore K_NOP in Insert mode. (closes #2379)
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 02d03b4..4202b03 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -417,12 +417,12 @@
 
 	cursorcmd();		/* set the cursor on the right spot */
 
-	/* Get a character.  Ignore K_IGNORE, it should not do anything, such
-	 * as stop completion. */
+	/* Get a character.  Ignore K_IGNORE and K_NOP, they should not do
+	 * anything, such as stop completion. */
 	do
 	{
 	    c = safe_vgetc();
-	} while (c == K_IGNORE);
+	} while (c == K_IGNORE || c == K_NOP);
 
 	if (KeyTyped)
 	{