return "No data points" when data is missing

[kevinschoon]

Hi --

This causes the chart to return "No data points" instead of a JS error in the following conditions:

• No data is returned from a given query
• The data returned does not have OHLC aliases

The result looks like this:

Have been waiting for a plugin like this for a while, really appreciate your contribution!

[ilgizar]

@kevinschoon, thanks for this improvement. I ask you to resolve the conflict before merge.

[kevinschoon]

@ilgizar Resolved the conflict and fixed some linting issues.

[ilgizar]

@kevinschoon Thank you, good work.