pbxFileReferenceObj: Made path property optional.

Author: sidneys

lib/pbxProject.js

@@ -1053,7 +1053,10 @@ function pbxFileReferenceObj(file) {
     obj.lastKnownFileType = file.lastType;
 
     obj.name = "\"" + file.basename + "\"";
+
+    if (file.path) {
         obj.path = "\"" + file.path.replace(/\\/g, '/') + "\"";
+    }
 
     obj.sourceTree = file.sourceTree;