fix(convert): do not return error when converting zero to float

[PetrHeinz]

Summary

Fixes a little edge case of to_float("0") returning an error. While 0 is not normal, it's commonly used in data parsed by Vector, and should not trigger an error.

This change will not re-introduce vectordotdev#1107 which was the main reason behind the original fix in vectordotdev#1108.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

How did you test this PR?

Modified the tests

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on
  our guidelines.
• No. A maintainer will apply the "no-changelog" label to this PR.

Checklist

• Our CONTRIBUTING.md is a good starting place.
• If this PR introduces changes to LICENSE-3rdparty.csv, please
  run dd-rust-license-tool write and commit the changes. More details here.
• For new VRL functions, please also create a sibling PR in Vector to document the new function.

References

• Closes: Function to_float fails to parse "0": Invalid float "0": not a normal f64 number vectordotdev/vector#21970

• Changes behavior of: fix(convert): return error when conversion exceeds f64 bounds vectordotdev/vrl#1108

[PetrHeinz]

Sorry for the brevity, just tried to suggest a quick fix through the web GUI 🙌

No worries if not up to the contrib-guide and gets closed 🤷

[PetrHeinz]

Original pr introducing the validation was reverted in vectordotdev#1179