Fix calloop double borrows

[kchibisov]

Fixes #109.

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Based on #110.

[codecov[bot]]

Codecov Report

Base: 89.17% // Head: 89.37% // Increases project coverage by +0.20% :tada:

Coverage data is based on head (e5983e1) compared to base (2089fa4). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #115 +/- ## ========================================== + Coverage 89.17% 89.37% +0.20% ========================================== Files 17 17 Lines 1699 1731 +32 ========================================== + Hits 1515 1547 +32 Misses 184 184 ``` | Flag | Coverage Δ | | |---|---|---| | macos-latest | `88.76% <100.00%> (+0.11%)` | :arrow_up: | | ubuntu-latest | `87.71% <100.00%> (+0.27%)` | :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=Smithay#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/Smithay/calloop/pull/115?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | Coverage Δ | | |---|---|---| | [src/loop\_logic.rs](https://codecov.io/gh/Smithay/calloop/pull/115/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL2xvb3BfbG9naWMucnM=) | `91.01% <100.00%> (+1.64%)` | :arrow_up: | | [src/sources/ping.rs](https://codecov.io/gh/Smithay/calloop/pull/115/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL3NvdXJjZXMvcGluZy5ycw==) | `85.71% <0.00%> (-14.29%)` | :arrow_down: | 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=Smithay). 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=Smithay)

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[elinorbgr]

Thanks!