email plugin: Include `stddef.h' which defines the `offsetof' macro.

diff --git a/src/email.c b/src/email.c
index f5a544a..869b7c3 100644 (file)
--- a/src/email.c
+++ b/src/email.c
@@ -39,6 +39,8 @@
 
 #include "configfile.h"
 
+#include <stddef.h>
+
 #if HAVE_LIBPTHREAD
 # include <pthread.h>
 #endif