Fix RTE sometimes inserting characters in wrong locations after multiple new lines

[aringenbach]

Fixes #7570

Edit: also fixes #7577 (since it's a single line change) Issue description here: https://github.com/vector-im/element-ios/pull/7583#pullrequestreview-1474583976

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 :warning:

Comparison is base (3cdedd6) 12.36% compared to head (8b43fcb) 12.36%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #7590 +/- ## =========================================== - Coverage 12.36% 12.36% -0.01% =========================================== Files 1648 1648 Lines 163667 163667 Branches 67211 67211 =========================================== - Hits 20242 20239 -3 - Misses 142760 142763 +3 Partials 665 665 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `6.21% <0.00%> (ø)` | | 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=vector-im#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://app.codecov.io/gh/vector-im/element-ios/pull/7590?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im) | Coverage Δ | | |---|---|---| | [Riot/Managers/Call/CallPresenter.swift](https://app.codecov.io/gh/vector-im/element-ios/pull/7590?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im#diff-UmlvdC9NYW5hZ2Vycy9DYWxsL0NhbGxQcmVzZW50ZXIuc3dpZnQ=) | `6.21% <0.00%> (ø)` | | | [Riot/Modules/Room/RoomViewController.m](https://app.codecov.io/gh/vector-im/element-ios/pull/7590?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im#diff-UmlvdC9Nb2R1bGVzL1Jvb20vUm9vbVZpZXdDb250cm9sbGVyLm0=) | `0.00% <0.00%> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/vector-im/element-ios/pull/7590/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im)

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[sonarcloud[bot]]

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