style(boa): minor cleanup

[neeldug]

It changes the following:

• extracts return from if let statement
• fixes clippy error in nightly

[codecov]

Codecov Report

Merging #838 into master will not change coverage.
The diff coverage is 71.42%.

@@           Coverage Diff           @@
##           master     #838   +/-   ##
=======================================
  Coverage   59.37%   59.37%           
=======================================
  Files         157      157           
  Lines       10036    10036           
=======================================
  Hits         5959     5959           
  Misses       4077     4077           

Impacted Files	Coverage Δ
boa/src/builtins/number/mod.rs	60.56% <50.00%> (ø)
boa/src/builtins/array/mod.rs	72.70% <100.00%> (ø)

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