fix: encode overlay options correctly

Author: malcolm-kee

lib/Server.js

@@ -672,6 +672,7 @@ class Server {
             typeof client.overlay === "boolean"
               ? String(client.overlay)
               : JSON.stringify({
+                  ...client.overlay,
                   errors: encodeOverlaySettings(client.overlay.errors),
                   warnings: encodeOverlaySettings(client.overlay.warnings),
                   runtimeErrors: encodeOverlaySettings(
@@ -2656,6 +2657,7 @@ class Server {
             "overlay",
             typeof overlayConfig === "object"
               ? {
+                  ...overlayConfig,
                   errors:
                     overlayConfig.errors &&
                     encodeOverlaySettings(overlayConfig.errors),