display gets corrupted on bogus data

[5chdn]

Reopen https://github.com/goerli/netstats-server/issues/13 by @veox

Most commonly visible on bar-graphs for block time, difficulty, transaction count...

The most common cause is someone accidentally connecting a node from network X to dashboard of network Y; but this could also happen due to malice.

In general, the dashboard is overly trusting in accepting the data fed to it as correct, and does not gracefully handle conflicts.