Fixed DebuggerClient.resume acting like stepInto

Fixed the code adding maxStringLength to V8 requests, so that it
no longer creates a new args object when the caller did not provide
one.

lib/DebuggerClient.js

@@ -87,7 +87,11 @@ DebuggerClient.prototype.request = function(command, args, callback) {
     };
   }
 
-  args = extend({ maxStringLength: 10000 }, args);
+  // Note: we must not add args object if it was not sent.
+  // E.g. resume (V8 request 'continue') does no work
+  // correctly when args are empty instead of undefined
+  if (args && args.maxStringLength == null)
+    args.maxStringLength = 10000;
 
   this._conn.request(command, { arguments: args }, function(response) {
     var refsLookup;