(hdb_read_master_key): set mkey to NULL before doing anything else

git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@8590 ec53bebd-3082-4978-b11e-865c3cabbd6b

lib/hdb/mkey.c

@@ -218,6 +218,8 @@ hdb_read_master_key(krb5_context context, const char *filename,
 
     off_t len;
 
+    *mkey = NULL;
+
     if(filename == NULL)
 	filename = HDB_DB_DIR "/m-key";