CLJS-672: source maps + optimizations + :libs breaks building

Only copy over files to the output directory if the js file record
contains :source-url information.

Author: swannodette

src/clj/cljs/closure.clj

@@ -890,15 +890,18 @@
     (if (or (not url)
             (= (.getProtocol url) "jar"))
       (write-javascript opts js)
+      ;; always copy original sources to the output directory
+      ;; when source maps enabled
       (let [out-file (if-let [ns (and (:source-map opts)
                                       (first (:provides js)))]
                        (io/file (io/file (output-directory opts))
-                         (ana/ns->relpath ns)))]
-        (when (and out-file
+                         (ana/ns->relpath ns)))
+            source-url (:source-url js)]
+        (when (and out-file source-url
                    (or (not (.exists ^File out-file))
-                       (> (.lastModified (io/file (:source-url js)))
+                       (> (.lastModified (io/file source-url))
                           (.lastModified out-file))))
-          (spit out-file (slurp (:source-url js))))
+          (spit out-file (slurp source-url)))
         js))))
 
 (comment