patch 8.2.4685: when a swap file is found for a popup there is no dialog

Problem:    When a swap file is found for a popup there is no dialog and the
            buffer is loaded anyway.
Solution:   Silently load the buffer read-only. (closes #10073)
diff --git a/src/buffer.c b/src/buffer.c
index 8b50540..bd37830 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -150,7 +150,8 @@
 	aco_save_T	aco;
 
 	aucmd_prepbuf(&aco, buf);
-	swap_exists_action = SEA_NONE;
+	if (swap_exists_action != SEA_READONLY)
+	    swap_exists_action = SEA_NONE;
 	open_buffer(FALSE, NULL, 0);
 	aucmd_restbuf(&aco);
     }
@@ -1053,10 +1054,12 @@
     int		count)
 {
     bufref_T	old_curbuf;
+    int		save_sea = swap_exists_action;
 
     set_bufref(&old_curbuf, curbuf);
 
-    swap_exists_action = SEA_DIALOG;
+    if (swap_exists_action == SEA_NONE)
+	swap_exists_action = SEA_DIALOG;
     (void)do_buffer(*eap->cmd == 's' ? DOBUF_SPLIT : DOBUF_GOTO,
 					     start, dir, count, eap->forceit);
     if (swap_exists_action == SEA_QUIT && *eap->cmd == 's')
@@ -1071,7 +1074,7 @@
 
 	// Quitting means closing the split window, nothing else.
 	win_close(curwin, TRUE);
-	swap_exists_action = SEA_NONE;
+	swap_exists_action = save_sea;
 	swap_exists_did_quit = TRUE;
 
 #if defined(FEAT_EVAL)