screencast: Fix region screencasts top coordinate

We don't need to invert the top as the ortho already is on the correct coordinate
space.

Thanks to Dominique Hummel for helping debug the issue!

src/plugins/screencast/regionscreencastsource.cpp

@@ -55,6 +55,7 @@ void RegionScreenCastSource::updateOutput(Output *output)
         QMatrix4x4 projectionMatrix;
         projectionMatrix.ortho(m_region);
         projectionMatrix.translate(outputGeometry.left() / m_scale, (m_region.bottom() - outputGeometry.bottom()) / m_scale);
+        projectionMatrix.translate(0, m_region.top() / m_scale);
 
         shaderBinder.shader()->setUniform(GLShader::ModelViewProjectionMatrix, projectionMatrix);