[FIX] calendar chart: skip missing value tooltips

[dhrp-odoo]

Description:

Calendar chart datasets use data as a Chart.js rendering payload, where every bucket is drawn with a constant value. The actual cell values are stored separately in values, which is only used by our tooltips and show-values plugin.

Before this commit, missing calendar values were stored as NaN in values. This is the right sentinel for Chart.js data points, but not for this metadata: the tooltip filter only skips undefined, so missing buckets still displayed a tooltip and formatted NaN as 1.00e-NaN.

This commit stores missing calendar metadata as undefined, keeping empty buckets out of tooltips/show-values while preserving real numeric values.

Task: 6276800

review checklist

• feature is organized in plugin, or UI components
• support of duplicate sheet (deep copy)
• in model/core: ranges are Range object, and can be adapted (adaptRanges)
• in model/UI: ranges are strings (to show the user)
• undo-able commands (uses this.history.update)
• multiuser-able commands (has inverse commands and transformations where needed)
• new/updated/removed commands are documented
• exportable in excel
• translations (_t("qmsdf %s", abc))
• unit tested
• clean commented code
• track breaking changes
• doc is rebuild (npm run doc)
• status is correct in Odoo

[robodoo]