Improved traceback when exception occurred during missing cache hit

[codecov[bot]]

Codecov Report

Base: 87.84% // Head: 87.84% // Increases project coverage by +0.00% :tada:

Coverage data is based on head (5190135) compared to base (a1b1235). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #298 +/- ## ======================================= Coverage 87.84% 87.84% ======================================= Files 69 69 Lines 10331 10334 +3 ======================================= + Hits 9075 9078 +3 Misses 1256 1256 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `87.84% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zwicker-group#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/zwicker-group/py-pde/pull/298?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zwicker-group) | Coverage Δ | | |---|---|---| | [pde/tools/cache.py](https://codecov.io/gh/zwicker-group/py-pde/pull/298/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zwicker-group#diff-cGRlL3Rvb2xzL2NhY2hlLnB5) | `94.46% <100.00%> (+0.07%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zwicker-group). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=zwicker-group)

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