patch 9.0.0308: when cmdheight is zero the attention prompt doesn't show

Problem:    When cmdheight is zero the attention prompt doesn't show.
Solution:   Do not use the message window for a prompt.

src/memline.c

@@ -4640,6 +4640,7 @@ attention_message(
     stat_T	st;
     time_t	swap_mtime;
 
+    dont_use_message_window();
     ++no_wait_return;
     (void)emsg(_(e_attention));
     msg_puts(_("\nFound a swap file by the name \""));

src/message.c

@@ -1443,6 +1443,19 @@ use_message_window(void)
 #endif
 }
 
+/*
+ * Do not use the message window for the next message(s).
+ * Used when giving a prompt.
+ */
+    void
+dont_use_message_window(void)
+{
+#ifdef HAS_MESSAGE_WINDOW
+    popup_hide_message_win();
+    cmdline_row = Rows - 1;
+#endif
+}
+
 /*
  * Prepare for outputting characters in the command line.
  */
@@ -4073,6 +4086,7 @@ do_dialog(
     }
 #endif
 
+    dont_use_message_window();
     oldState = State;
     State = MODE_CONFIRM;
     setmouse();

src/proto/message.pro

@@ -24,6 +24,7 @@ void wait_return(int redraw);
 void set_keep_msg(char_u *s, int attr);
 void set_keep_msg_from_hist(void);
 int use_message_window(void);
+void dont_use_message_window(void);
 void msg_start(void);
 void msg_starthere(void);
 void msg_putchar(int c);

src/version.c

@@ -707,6 +707,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    308,
 /**/
     307,
 /**/