patch 7.4.2101
Problem:    Looping over windows, buffers and tab pages is inconsistant.
Solution:   Use FOR_ALL_ macros everywhere. (Yegappan Lakshmanan)
diff --git a/src/memfile.c b/src/memfile.c
index e2fadc2..4a48430 100644
--- a/src/memfile.c
+++ b/src/memfile.c
@@ -796,7 +796,7 @@
     if (mfp->mf_fd < 0 && need_release && p_uc)
     {
 	/* find for which buffer this memfile is */
-	for (buf = firstbuf; buf != NULL; buf = buf->b_next)
+	FOR_ALL_BUFFERS(buf)
 	    if (buf->b_ml.ml_mfp == mfp)
 		break;
 	if (buf != NULL && buf->b_may_swap)
@@ -861,7 +861,7 @@
     bhdr_T	*hp;
     int		retval = FALSE;
 
-    for (buf = firstbuf; buf != NULL; buf = buf->b_next)
+    FOR_ALL_BUFFERS(buf)
     {
 	mfp = buf->b_ml.ml_mfp;
 	if (mfp != NULL)