Fix calloop double borrows take two

[kchibisov]

This is a follow up to 1787237a21aa0eb44676f255dfa26e5a2a74b5df given that one source could be removed from another we can't operate on keys.

--

@elinorbgr I'm not quite sure if that's what you meant in matrix, but I'd ask the user to try repro with that patch.

[codecov[bot]]

Codecov Report

Base: 89.31% // Head: 89.44% // Increases project coverage by +0.13% :tada:

Coverage data is based on head (1eb880e) compared to base (1787237). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #117 +/- ## ========================================== + Coverage 89.31% 89.44% +0.13% ========================================== Files 17 17 Lines 1731 1715 -16 ========================================== - Hits 1546 1534 -12 + Misses 185 181 -4 ``` | Flag | Coverage Δ | | |---|---|---| | macos-latest | `88.98% <100.00%> (+0.29%)` | :arrow_up: | | ubuntu-latest | `87.57% <100.00%> (-0.14%)` | :arrow_down: | 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/117?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/117/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL2xvb3BfbG9naWMucnM=) | `90.43% <100.00%> (-0.20%)` | :arrow_down: | | [src/sys/mod.rs](https://codecov.io/gh/Smithay/calloop/pull/117/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL3N5cy9tb2QucnM=) | `91.59% <0.00%> (+0.84%)` | :arrow_up: | | [src/sources/ping/pipe.rs](https://codecov.io/gh/Smithay/calloop/pull/117/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL3NvdXJjZXMvcGluZy9waXBlLnJz) | `98.55% <0.00%> (+1.44%)` | :arrow_up: | | [src/sources/ping.rs](https://codecov.io/gh/Smithay/calloop/pull/117/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL3NvdXJjZXMvcGluZy5ycw==) | `100.00% <0.00%> (+14.28%)` | :arrow_up: | 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)

:umbrella: View full report at Codecov.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.

[elinorbgr]

Thanks, LGTM.