[pgAdmin4][Patch]: TypeError: Cannot read property 'generate_url' of undefined

Issue: When any of the docked tab(statistics, dependents & dependencies) are clicked without selecting any tree node. it gives error in browser console panel.

Because the node passed is undefined. and check is missing. This is now fixed by adding check for node passed.

So, please review the attached patch for the fix.

Thanks,

Surinder Kumar