make REPL bootstrap helper idempotent - don't try to backup goog.isProvided_ or goog.require if already done

Author: swannodette

script/test

@@ -22,6 +22,7 @@ if ! bin/cljsc src/test/cljs "{:optimizations :advanced
                                :npm-deps {:lodash \"4.17.4\"}
                                :closure-warnings {:non-standard-jsdoc :off :global-this :off}
                                :install-deps true
+                               :pseudo-names true
                                :language-in :es6
                                :language-out :es5
                                :foreign-libs [{:file \"src/test/cljs/calculator_global.js\"

src/main/clojure/cljs/repl/bootstrap.clj

@@ -17,12 +17,14 @@
   ;; we never care how many times a namespace is loaded it doesn't matter if
   ;; Google Closure Library or ClojureScript
   (repl/evaluate-form repl-env env "<cljs repl>"
-    '(set! (.-isProvided__ js/goog) js/goog.isProvided_))
+    '(when-not (.-isProvided__ js/goog)
+       (set! (.-isProvided__ js/goog) js/goog.isProvided_)))
   (repl/evaluate-form repl-env env "<cljs repl>"
     '(set! (.-isProvided_ js/goog) (fn [x] false)))
   ;; monkey-patch goog.require
   (repl/evaluate-form repl-env env "<cljs repl>"
-    '(set! (.-require__ js/goog) js/goog.require))
+    '(when-not (.-require__ js/goog)
+       (set! (.-require__ js/goog) js/goog.require)))
   (repl/evaluate-form repl-env env "<cljs repl>"
     '(set! (.-require js/goog)
        (fn [src reload]