Boolean fix.

Fixes logic when document.currentScript is undefined.

Error introduced in 100331.

Change-Id: Id309975be44f97094c8068afca892333de197690
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js
index 8f78dd3..1fac076 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js
@@ -255,7 +255,7 @@
 
     // TODO(andybons): Polyfill currentScript for IE10/11 (edge supports it).
     const src = opt_src || (document.currentScript &&
-         document.currentScript.src || document.currentScript.baseURI);
+         (document.currentScript.src || document.currentScript.baseURI));
     const plugin = new Plugin(src);
     try {
       callback(plugin);