patch 9.0.0980: the keyboard state response may end up in a shell command

Problem:    The keyboard state response may end up in a shell command.
Solution:   Only request the keyboard protocol state when the typeahead is
            empty, no more commands are following and not exiting.  Add the
            t_RK termcap entry for this.

src/ex_getln.c

@@ -2908,6 +2908,9 @@ getexmodeline(
 	long    sw;
 	char_u *s;
 
+	// May request the keyboard protocol state now.
+	may_send_t_RK();
+
 	if (ga_grow(&line_ga, 40) == FAIL)
 	    break;