Fix buffer size error

The hexadecimal representation of a SHA2-256 hash needs 64 bytes,
not 32.

src/secretcfg.c

@@ -410,7 +410,7 @@ int
 gfsec_write_config(gfsec_secret_t *cfg, const char *filename)
 {
     FILE *f;
-    char buffer[33];
+    char buffer[65];
     unsigned n, m;
 
     static char *schemes[] = { "file://", "uuid://", "label://", "mtp://" };