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)

Author: brammool

src/main.c

@@ -1432,9 +1432,14 @@ getout(int exitval)
 		buf = wp->w_buffer;
 		if (CHANGEDTICK(buf) != -1)
 		{
+		    bufref_T bufref;
+
+		    set_bufref(&bufref, buf);
 		    apply_autocmds(EVENT_BUFWINLEAVE, buf->b_fname,
 						    buf->b_fname, FALSE, buf);
-		    CHANGEDTICK(buf) = -1;  /* note that we did it already */
+		    if (bufref_valid(&bufref))
+			CHANGEDTICK(buf) = -1;  /* note we did it already */
+
 		    /* start all over, autocommands may mess up the lists */
 		    next_tp = first_tabpage;
 		    break;

src/version.c

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