an empty chart causes keikai to stop working

Steps to Reproduce

1. load the attached file

Current Result

keikai keep showing "processing" message and a request never gets a response
any edit operation doesn't work

Expected Result

• keikai still works normally.
• show an empty chart with "no data" label.

Debug Information

• a browser renders a sheet partially. when firing onZSSFetchActiveRange, the request is pending and never gets response.
• the file contains an empty chart which causes an infinite loop in HighchartsAxisHelper.setupAxis()
• Excel will show nothing until a user selects the chart. If the empty chart is covered by another correct chart, it's hard for a user to spot the empty chart. It's better to show an empty chart with "no data", so that a user can easily spot the empty chart. Because it's very likely an invalid, useless chart.

Workaround

1. fill empty cells with 0
2. delete the chart