mexport: ensure mbox entries are separated by an empty line

https://www.loc.gov/preservation/digital/formats/fdd/fdd000383.shtml
> Each message is immediately prefaced by a separation line and
> terminated by an empty line.

Bug discovered by skarnet.

1 files changed, 3 insertions, 0 deletions

diff --git a/mexport.c b/mexport.c
index d758d0c..27dc40f 100644
--- a/mexport.c
+++ b/mexport.c
@@ -125,6 +125,9 @@ export(char *file)
 	if (!final_nl)
 		putchar('\n');
 
+	// ensure empty line at end of message
+	putchar('\n');
+
 	fclose(infile);
 }