fix(compiler): reduce empty array without init val

[thevilledev]

Motivation

Fuzzing discovered a panic in #908 on an unrelated change. The full run logs can be found here but the gist of it:

runtime error: index out of range [0] with length 0 (1:1)
 | reduce(9..0,357)
 | ^
panic: errorf [recovered]
	panic: errorf

This issue is triggered when reduce is called on an empty array without an initial value (e.g., reduce(9..0, # + #acc)). The compiler emits code that accessed the first element before checking if the array was empty.

Changes

• Emit a bounds check before accessing the first array element when reduce has no initial value, throwing a descriptive error if the array is empty
• Add regression tests for the error case and for reduce with initial value on empty arrays
• Add the new error message to the fuzz test skip list

Further comments

The optimizer correctly skips optimization for reversed ranges (like 10..1) and delegates to runtime. This fix ensures the runtime handles empty arrays gracefully instead of panicking.