Factor shadow constants out of MainShaderConstantSetter

src/client/shadows/dynamicshadowsrender.h

@@ -27,6 +27,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 class ShadowDepthShaderCB;
 class shadowScreenQuad;
 class shadowScreenQuadCB;
+class IWritableShaderSource;
 
 enum E_SHADOW_MODE : u8
 {
@@ -54,9 +55,13 @@ class ShadowRenderer
 	static const int TEXTURE_LAYER_SHADOW = 3;
 
 	ShadowRenderer(IrrlichtDevice *device, Client *client);
-
 	~ShadowRenderer();
 
+	// Call before generating any shaders
+	// This is required because this class is initialized much later than all
+	// the shaders are dealt with.
+	static void preInit(IWritableShaderSource *shsrc);
+
 	void initialize();
 
 	/// Adds a directional light shadow map (Usually just one (the sun) except in