Allow disconnections to be signaled by drivers

This allows for disconnections to be detected quickly
where possible.

It also makes sure other driver errors aren't thrown
in the event of a disconnection.

include/icsneo/platform/posix/ftdi.h

@@ -19,7 +19,7 @@ public:
 	static std::vector<neodevice_t> FindByProduct(int product);
 
 	FTDI(const device_eventhandler_t& err, neodevice_t& forDevice);
-	~FTDI() { close(); }
+	~FTDI() { if(isOpen()) close(); }
 	bool open();
 	bool close();
 	bool isOpen() { return ftdi.isOpen(); }

include/icsneo/platform/posix/stm32.h

@@ -24,6 +24,7 @@ public:
 	 * Other POSIX systems (BSDs, QNX, etc) will need bespoke code written in the future
 	 */
 	STM32(const device_eventhandler_t& err, neodevice_t& forDevice) : Driver(err), device(forDevice) {}
+	~STM32() { if(isOpen()) close(); }
 	static std::vector<neodevice_t> FindByProduct(int product);
 
 	bool open();
@@ -38,6 +39,7 @@ private:
 
 	void readTask();
 	void writeTask();
+	bool fdIsValid();
 };
 
 }