- track level start time for the shader system, reset the shaders.

src/p_setup.cpp

@@ -3627,6 +3627,8 @@ void P_SetupLevel (const char *lumpname, int position)
 	bool buildmap;
 	const int *oldvertextable = NULL;
 
+	level.ShaderStartTime = I_msTime(); // indicate to the shader system that the level just started
+
 	// This is motivated as follows:
 
 	bool RequireGLNodes = Renderer->RequireGLNodes() || am_textured;