[TSVB] Adding check for model and visData

[simianhacker]

This PR adds a check for the model and visData properties. These two values should essentially never be null. Due to a recent PR there is now a race condition which requires us to check to make sure these values are valid before rendering the rest of the React tree.

[ppisljar]

this is the PR that broke this: #13742

• visualization's constructor will get called during initialization
• if visualization controler has an init function it will get called (it should return a promise)
• once the init function promise is resolved (or if no init function straight away) vis.initialized is set
• after vis.initialized is set the request is executed (to ES)
• after data is received the render function is called (with params and visData)

however in the editor example it goes a bit differently:

• editor constructor gets called
• editors render method gets called
• editor will probably init the visualization (and if not it should set vis.initialized itself)
  the normal flow described above follows.
  ... after data is received editor render method gets called again with the data

in this PR #13779 tsvb editor sets the vis.initialized in its constructor. now the race condition starts.

• editor render method will get called right after the constructor is executed
• but request to ES already started and when we get response editor render method will get called with data

i think this should be fixed on visualize side. editors render method (the first time, without data) should not be called if editor set the vis.initialized in constructor (which means request to backend is pending)

pr to do that: #13858

[ppisljar]

LGTM, but maybe its not needed after we address the issue in visualize

[simianhacker]

it's probably not as necessary but I think it's good to have these checks.

[simianhacker]

Back ported to 6.0 with ad6f53e
Back ported to 6.x with 4c538fe