FifoBuffer.advance method not throw exception when length==0 (#3641)

* fifobuffer not throw error when length = 0

* Update FIFOBuffer.h

fix indentation

Co-authored-by: Aleksandar Fabijanic <aleks-f@users.noreply.github.com>

Foundation/include/Poco/FIFOBuffer.h

@@ -334,6 +334,7 @@ public:
 		/// Should be called AFTER the data 
 		/// was copied into the buffer.
 	{
+		if (0 == length) return;
 		Mutex::ScopedLock lock(_mutex);
 
 		if (length > available())