skip price spike check if prices are zero

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81.94%. Comparing base (f3b5e9d) to head (4f1e018). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/agent0/hyperfuzz/system_fuzz/invariant_checks.py	50.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1695 +/- ## ========================================== + Coverage 81.56% 81.94% +0.37% ========================================== Files 99 99 Lines 7655 7659 +4 ========================================== + Hits 6244 6276 +32 + Misses 1411 1383 -28 ``` | [Flag](https://app.codecov.io/gh/delvtech/agent0/pull/1695/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=delvtech) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/delvtech/agent0/pull/1695/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=delvtech) | `81.94% <50.00%> (+0.37%)` | :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=delvtech#carryforward-flags-in-the-pull-request-comment) to find out more.

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