[platform] CANUSB: add missing mutex usage

I was not able to receive messages from a CAN2USB. The mutex was already
added but newer used.

Author: strongly-typed

src/modm/platform/can/canusb/canusb.hpp

@@ -53,7 +53,8 @@ class CanUsb : public ::modm::Can
 	inline bool
 	isMessageAvailable()
 	{
-		return (!this->readBuffer.empty());
+		MutexGuard stateGuard(readBufferLock);
+		return (not this->readBuffer.empty());
 	}
 
 	bool

src/modm/platform/can/canusb/canusb_impl.hpp

@@ -180,6 +180,7 @@ template <typename SerialPort>
 bool
 modm::platform::CanUsb<SerialPort>::getMessage(can::Message& message)
 {
+	MutexGuard stateGuard(readBufferLock);
 	if (not this->readBuffer.empty())
 	{
 		message = this->readBuffer.front();
@@ -229,6 +230,7 @@ modm::platform::CanUsb<SerialPort>::update()
 			if (modm::CanLawicelFormatter::convertToCanMessage(
 					this->tmpRead.c_str(), message))
 			{
+				MutexGuard stateGuard(readBufferLock);
 				this->readBuffer.push(message);
 			}
 		}