WIP: Skip adding a defined name if the sheet isn't found

[vhr]

This is:

- [x] a bugfix
- [ ] a new feature

Checklist:

• Changes are covered by unit tests
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change
• Documentation is updated as necessary

Why this change is needed?

in case when in the xlsx file has unused range name and the library will throw a exception with the following message as below, every time when we try to read the file

You must specify a worksheet or a scope for a Named Range

[oleibman]

I believe that PR #1742 accomplishes the same goal, in a manner consistent with how Excel operates.