refactor(ironrdp-web): fix `indexing_slicing` clippy lint warnings

[RRRadicalEdward]

This lint

Checks for usage of indexing or slicing that may panic at runtime.

This one is quite pedantic and changes the way we write the code, but on the other hand, it makes the code more panic-resistant. Fixed the lint warnings only for ironrdp-web to see early feedback on it. If we agree on adding it, I will add this lint for each crate separately, because there are too many warnings to do in 1 PR:

[github-actions[bot]]

Coverage Report :robot: :gear:

Past: Total lines: 30217 Covered lines: 18800 (62.22%)

New: Total lines: 30217 Covered lines: 18800 (62.22%)

Diff: +0.00%

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[RRRadicalEdward]

@CBenoit Does it look good? Should we proceed with adding this lint?

[CBenoit]

I want to double check a little bit more before merging this.

[CBenoit]

I’m putting back this PR on my TODO review list.