Fix CChan::TrimBuffer() (#63)

CChan::TrimBuffer() was trying to do "m_vsBuffer.begin() + -<some number>" which would cause a segmentation fault

Fixes #63

Chan.cpp

@@ -535,7 +535,7 @@ void CChan::ClearBuffer() {
 
 void CChan::TrimBuffer(const unsigned int uMax) {
 	if (m_vsBuffer.size() > uMax) {
-		m_vsBuffer.erase(m_vsBuffer.begin(), m_vsBuffer.begin() + (uMax - m_vsBuffer.size()));
+		m_vsBuffer.erase(m_vsBuffer.begin(), m_vsBuffer.begin() + (m_vsBuffer.size() - uMax));
 	}
 }