Fixes issue on breakpoint resume where console was not open upon pausing...

... but opened while paused. Or any other case where either args or args.maxStringLength is not defined.


<b>Reproduction:</b>
   
Using master 127955f6005c8cbd1c872d01e69149d54b9863ad

1. With the console closed / minimized, set a breakpoint somewhere in the Sources section of the debugger client.
2. In the debugged application, do something that traverses the breakpoint
--> AUT execution pauses, debugger client shows paused. Console is still minimized.
3. Open the console in the debugger client.
4. Click the button to resume execution.

<b>Result:</b>

Error / crash:
```
/usr/local/lib/node_modules/node-inspector/lib/DebuggerClient.js:89
  args.maxStringLength = 10000;
                       ^
TypeError: Cannot set property 'maxStringLength' of undefined
    at DebuggerClient.request (/usr/local/lib/node_modules/node-inspector/lib/DebuggerClient.js:90:24)
    at Object.DebuggerAgent._sendContinue (/usr/local/lib/node_modules/node-inspector/lib/DebuggerAgent.js:132:26)
  ...
```

So this change should protect against that or any other similar cases. 

:zap: : I'm not sure how / if the test should be updated.