Fix link not found line numbers

[tristanlatr]

• Fix #745

[codecov[bot]]

Codecov Report

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

Comparison is base (922f81e) 92.69% compared to head (a15d419) 92.69%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #748 +/- ## ======================================= Coverage 92.69% 92.69% ======================================= Files 47 47 Lines 8284 8285 +1 Branches 1824 1826 +2 ======================================= + Hits 7679 7680 +1 Misses 347 347 Partials 258 258 ``` | [Files](https://app.codecov.io/gh/twisted/pydoctor/pull/748?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=twisted) | Coverage Δ | | |---|---|---| | [pydoctor/linker.py](https://app.codecov.io/gh/twisted/pydoctor/pull/748?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=twisted#diff-cHlkb2N0b3IvbGlua2VyLnB5) | `90.20% <100.00%> (+0.06%)` | :arrow_up: |

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