Fix crc validation

src/message.c

@@ -9,7 +9,8 @@ message_validate(const union Message* message) {
     if(message->header.crc != crc8(message, 3))
         return MESSAGEERR_HEADERCRC;
 
-    if(message->header.crc != crc16(message, length - sizeof(struct Footer)))
+    struct Footer* footer = (void*)message + length - sizeof(struct Footer);
+    if(footer->crc != crc16(message, length - sizeof(struct Footer)))
         return MESSAGEERR_FOOTERCRC;
 
     return MESSAGEERR_NONE;