fix: correct Live 24/7 handling and label regressions

- stream.updateWithIssue: 'Live 24/7: Yes' meant the stream IS 24/7, but it
  was assigned straight to isNot247, inverting the label. A 'No' answer was
  also ignored because the guard skipped falsy values.
- dataSet.getBoolean: an unanswered dropdown is stored as '' by
  parseIssueBody, which getBoolean read as false. Treat it as undefined so
  'no answer' means 'leave unchanged' instead of 'Not 24/7'.
- update.addStream: has() is true for an unanswered field, so it produced
  isNot247 = true for issues that left the dropdown blank.
- generate: sortBy got five orders for four iteratees.
- 2_streams_edit.yml: restore the '~' reset option dropped from the quality
  dropdown when the Label field was removed.
- stream.getLabels: use const to satisfy prefer-const.

scripts/core/dataSet.ts

@@ -23,9 +23,11 @@ export class DataSet {
   }
 
   getBoolean(key: string): boolean | undefined {
-    if (this.missing(key)) return undefined
+    const value = this._data.get(key)
 
-    return this._data.get(key) === 'TRUE' ? true : false
+    if (value === undefined || value === '') return undefined
+
+    return value === 'TRUE'
   }
 
   getString(key: string): string | undefined {