Move callback outside of try.

Leaving the callback inside try leads to any programmer error inside the callback being captured
and the callback re-called with that as an error.

In normal nodejs flow this may turn into an infinite loop.
In promisified flow this leads to cryptic errors about callback being called twice.

src/util.js

@@ -134,12 +134,12 @@ util.getTextReplacement = function( src, relativeTo, callback )
         try
         {
             var replacement = util.getInlineFileContents( src, relativeTo );
-            return callback( null, replacement );
         }
         catch( err )
         {
             return callback( err );
         }
+        return callback( null, replacement );
     }
 };