Better error when starting a session without a port

[rllola]

When creating a new session with joystream-node it is required to have a port given. If not given the error is not very explicit about what is happening.

TypeError: Cannot match against 'undefined' or 'null'.
    at Session (/home/lola/Workspace/JoyStream/joystream-electron/node_modules/joystream-node/dist/Session.js:21)
    at new Stream (Stream.js [sm]:13)
    at /home/lola/Workspace/JoyStream/joystream-electron/node_modules/react-dom/lib/ReactCompositeComponen…:294
    at measureLifeCyclePerf (/home/lola/Workspace/JoyStream/joystream-electron/node_modules/react-dom/lib/ReactCompositeComponen…:75)
    at ReactCompositeComponentWrapper._constructComponentWithoutOwner (/home/lola/Workspace/JoyStream/joystream-electron/node_modules/react-dom/lib/ReactCompositeComponen…:293)
    at ReactCompositeComponentWrapper._constructComponent (/home/lola/Workspace/JoyStream/joystream-electron/node_modules/react-dom/lib/ReactCompositeComponen…:279)
    at ReactCompositeComponentWrapper.mountComponent (/home/lola/Workspace/JoyStream/joystream-electron/node_modules/react-dom/lib/ReactCompositeComponen…:187)
    at Object.mountComponent (/home/lola/Workspace/JoyStream/joystream-electron/node_modules/react-dom/lib/ReactReconciler.js:45)
    at ReactDOMComponent.mountChildren (/home/lola/Workspace/JoyStream/joystream-electron/node_modules/react-dom/lib/ReactMultiChild.js:236)
    at ReactDOMComponent._createInitialChildren (/home/lola/Workspace/JoyStream/joystream-electron/node_modules/react-dom/lib/ReactDOMComponent.js:703)

A default port should be used or a better error saying that port is required should be sent.

[bedeho]

Yes, a I think the type checking macro needs to include the variable name or something similar.