* Theme File Missing But Referenced in Spreadsheet
Fix#3770. A rels file points to a non-existent theme file in the spreadsheet. In other similar cases (e.g. PR #3771), Excel opens such a spreadsheet, but with an error pop-up. Not so with this file; it just opens the spreadsheet without the pop-up. PhpSpreadsheet will now account for this unusual situation as well.
* Update CHANGELOG.md
oleibman