inline coding of 0-length messages

Allows the processing of 0-length messages (which is true of some
important ones in the DSDL) to be optimized away.

Author: tpwrules

templates/msg.h.em

@@ -81,15 +81,32 @@ static inline uint32_t @(msg_underscored_name)_encode(@(msg_c_type)* msg, uint8_
     , bool tao
 #endif
 ) {
+@[if msg_max_bitlen == 0]
+    (void)msg;
+    (void)buffer;
+#if CANARD_ENABLE_TAO_OPTION
+    (void)tao;
+#endif
+
+    return 0; // 0-length message encodes to 0 bytes
+@[else]
     return _@(msg_underscored_name)_encode(msg, buffer
 #if CANARD_ENABLE_TAO_OPTION
     , tao
 #endif
     );
+@[end if]
 }
 
 static inline bool @(msg_underscored_name)_decode(const CanardRxTransfer* transfer, @(msg_c_type)* msg) {
+@[if msg_max_bitlen == 0]
+    (void)msg;
+
+    // all transports accurately convey a payload length of 0 bytes so any payload is an error
+    return transfer->payload_len != 0;
+@[else]
     return _@(msg_underscored_name)_decode(transfer, msg);
+@[end if]
 }
 
 #if defined(CANARD_DSDLC_INTERNAL)