updated for version 7.4.645

Problem:    When splitting the window in a BufAdd autocommand while still in
            the first, empty buffer the window count is wrong.
Solution:   Do not reset b_nwindows to zero and don't increment it.

src/buffer.c

@@ -1794,7 +1794,6 @@ buflist_new(ffname, sfname, lnum, flags)
 	if (aborting())		/* autocmds may abort script processing */
 	    return NULL;
 #endif
-	/* buf->b_nwindows = 0; why was this here? */
 	free_buffer_stuff(buf, FALSE);	/* delete local variables et al. */
 
 	/* Init the options. */
@@ -1872,6 +1871,9 @@ buflist_new(ffname, sfname, lnum, flags)
 #ifdef FEAT_AUTOCMD
     if (!(flags & BLN_DUMMY))
     {
+	/* Tricky: these autocommands may change the buffer list.  They could
+	 * also split the window with re-using the one empty buffer. This may
+	 * result in unexpectedly losing the empty buffer. */
 	apply_autocmds(EVENT_BUFNEW, NULL, NULL, FALSE, buf);
 	if (!buf_valid(buf))
 	    return NULL;

src/ex_cmds.c

@@ -3375,7 +3375,6 @@ do_ecmd(fnum, ffname, sfname, eap, newlnum, flags, oldwin)
 	if (buf->b_ml.ml_mfp == NULL)		/* no memfile yet */
 	{
 	    oldbuf = FALSE;
-	    buf->b_nwindows = 0;
 	}
 	else					/* existing memfile */
 	{
@@ -3408,7 +3407,7 @@ do_ecmd(fnum, ffname, sfname, eap, newlnum, flags, oldwin)
 	 * Make the (new) buffer the one used by the current window.
 	 * If the old buffer becomes unused, free it if ECMD_HIDE is FALSE.
 	 * If the current buffer was empty and has no file name, curbuf
-	 * is returned by buflist_new().
+	 * is returned by buflist_new(), nothing to do here.
 	 */
 	if (buf != curbuf)
 	{
@@ -3515,8 +3514,6 @@ do_ecmd(fnum, ffname, sfname, eap, newlnum, flags, oldwin)
 	    au_new_curbuf = NULL;
 #endif
 	}
-	else
-	    ++curbuf->b_nwindows;
 
 	curwin->w_pcmark.lnum = 1;
 	curwin->w_pcmark.col = 0;

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    645,
 /**/
     644,
 /**/