Fix vibe-d#2484 - clear m_fill on flush exception

stream/vibe/stream/wrapper.d

@@ -309,14 +309,15 @@ struct StreamOutputRange(OutputStream, size_t buffer_size = 256)
 
 	~this()
 	{
+		scope (failure) () @trusted { destroy(m_stream); }(); // workaround for #2484
 		flush();
 	}
 
 	void flush()
 	{
 		if (m_fill == 0) return;
+		scope (exit) m_fill = 0;
 		m_stream.write(m_data[0 .. m_fill]);
-		m_fill = 0;
 	}
 
 	void drop()