Explicitly dispose the event driver on thread shutdown.

Handle multiple calls to dispose() gracefully, because external code may already make an explicit call to dispose().

source/eventcore/core.d

@@ -30,6 +30,11 @@ static if (!is(NativeEventDriver == EventDriver)) {
 		if (!s_driver) s_driver = new NativeEventDriver;
 	}
 
+	static ~this()
+	{
+		s_driver.dispose();
+	}
+
 	shared static this()
 	{
 		s_driver = new NativeEventDriver;

source/eventcore/drivers/posix/driver.d

@@ -89,9 +89,11 @@ final class PosixEventDriver(Loop : PosixEventLoop) : EventDriver {
 
 	final override void dispose()
 	{
+		if (!m_loop) return;
 		m_files.dispose();
 		m_dns.dispose();
 		m_loop.dispose();
+		m_loop = null;
 	}
 }
 

source/eventcore/drivers/winapi/driver.d

@@ -72,7 +72,9 @@ final class WinAPIEventDriver : EventDriver {
 
 	override void dispose()
 	{
+		if (!m_events) return;
 		m_events.dispose();
+		m_events = null;
 		assert(threadInstance !is null);
 		threadInstance = null;
 	}