Fix crash on reload

src/RenderContext.cpp

@@ -215,6 +215,9 @@ void RenderContext::InitializeBuffers()
 	postprocessFs.Source(GLSLStrings(sources));
 	postprocessFs.Compile();
 
+	// Reset postprocess prog instance
+	postprocessProg = oglplus::Program();
+
 	postprocessProg.AttachShader(GetScreenQuadVertexShader());
 	postprocessProg.AttachShader(postprocessFs);