Harden window closing code upon session reset

[aik099]

Problems solved:

• initial window is closed upon session reset, when it's name was changed through the JavaScript after opening (Closes #25)
• an NoSuchWindow exception being thrown upon session reset, when initial window name was changed through the JavaScript after opening (Closes #26)

Test failure is unrelated.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 82.24%. Comparing base (71c242b) to head (d04dfda).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #27 +/- ## ============================================ - Coverage 83.65% 82.24% -1.42% + Complexity 192 191 -1 ============================================ Files 1 1 Lines 471 473 +2 ============================================ - Hits 394 389 -5 - Misses 77 84 +7 ```

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[aik099]

Thank you, @stof .