Fix potential bug when using multiple lights. (#1055)

crates/bevy_pbr/src/render_graph/forward_pipeline/forward.frag

@@ -53,6 +53,10 @@ void main() {
         // add light contribution
         color += diffuse * light.color.xyz;
     }
+
+    // average the lights so that we will never get something with > 1.0
+    color /= max(float(NumLights.x), 1.0);
+
     output_color.xyz *= color;
 # endif