Protect against NPE caused by null devtoolsServer

[kenzieschmoll]

@DanTup we were seeing exceptions in g3 because devToolsServer was null ("devtools server not available (204)" printed to console in this case).

This will fix the NPE but do we expect `devToolsServer to be null?

[devoncarew]

lgtm

I believe that devToolsServer will be null if devtools was not launched from the server. If that's not the case here, we may have a race condition.

[DanTup]

I think previously the catch block above would return and prevent all this code running. There are some changes in #1886 that allow connect() to log its own errors and return null though which break this. Change lgtm, though it might be cleaner to check for null further up and just return since it's likely none of this method is ever expected to run if there's no connection (this would prevent it coming back if there are further changes in this method that don't consider nulls).