mrp: Fix pairing requirement when disabled

[postlund]

Relates to #1567

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02 :tada:

Comparison is base (fef1667) 88.85% compared to head (c34a0cc) 88.87%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2099 +/- ## ========================================== + Coverage 88.85% 88.87% +0.02% ========================================== Files 162 162 Lines 10858 10862 +4 ========================================== + Hits 9648 9654 +6 + Misses 1210 1208 -2 ``` | [Impacted Files](https://app.codecov.io/gh/postlund/pyatv/pull/2099?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl) | Coverage Δ | | |---|---|---| | [pyatv/protocols/mrp/\_\_init\_\_.py](https://app.codecov.io/gh/postlund/pyatv/pull/2099?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl#diff-cHlhdHYvcHJvdG9jb2xzL21ycC9fX2luaXRfXy5weQ==) | `95.99% <100.00%> (+0.02%)` | :arrow_up: | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/postlund/pyatv/pull/2099/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pierre+St%C3%A5hl)

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