patch 8.0.1404: invalid memory access on exit

Problem:    Invalid memory access on exit when autocommands wipe out a buffer.
            (gy741, Dominique Pelle)
Solution:   Check if the buffer is still valid. (closes #2449)

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1404,
 /**/
     1403,
 /**/