patch 8.2.4613: return type of swapfile_unchanged() is wrong

Problem:    Return type of swapfile_unchanged() is wrong.
Solution:   Use "int". (closes #10000  Yeah!)
diff --git a/src/memline.c b/src/memline.c
index e1a4cb3..7b453cd 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -2261,7 +2261,7 @@
  * Return TRUE if the swap file looks OK and there are no changes, thus it can
  * be safely deleted.
  */
-    static time_t
+    static int
 swapfile_unchanged(char_u *fname)
 {
     stat_T	    st;