fix(abacus): fix bug to read the data when relax job not set cal_stress

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (8c653ba) 82.92% compared to head (7d8495b) 82.96%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## devel #549 +/- ## ========================================== + Coverage 82.92% 82.96% +0.03% ========================================== Files 73 73 Lines 6507 6510 +3 ========================================== + Hits 5396 5401 +5 + Misses 1111 1109 -2 ``` | [Files](https://app.codecov.io/gh/deepmodeling/dpdata/pull/549?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepmodeling) | Coverage Δ | | |---|---|---| | [dpdata/abacus/relax.py](https://app.codecov.io/gh/deepmodeling/dpdata/pull/549?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deepmodeling#diff-ZHBkYXRhL2FiYWN1cy9yZWxheC5weQ==) | `91.24% <100.00%> (+1.68%)` | :arrow_up: |

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