Php7 Problem with TemplateProcessor Destructor

[oleibman]

Description

A particularly perplexing problem accidentally introduced by PR #2475. Problem does not arise for Php8, and does not arise for Php7 unit tests. But, running not under Phpunit auspices with Php7 can cause a warning message at destructor time if the save function has been used. A very artificial test is introduced to test this situation.

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context.

Fixes # 2548

Checklist:

• [x] I have run composer run-script check --timeout=0 and no errors were reported
• [x] The new code is covered by unit tests (check build/coverage for coverage report)
• [ ] I have updated the documentation to describe the changes

[coveralls]

coverage: 97.218% (+0.001%) from 97.217% when pulling e295f8619735eaeb0968d48209189a0477f2eb6f on oleibman:word2548 into 2f4da6e491643c88f3c5d2892f5a63febb66b313 on PHPOffice:master.