Better error range for missing return

This typo makes full function body red:
```haxe
class Main {
static function main() {}

static function find(stacks:Array>, card:Int):Null {
for (stack in stacks) {
final last = stack[stack.length - 1];
if (card == last) {
return 0;
}
return null;
}
}
}
```
Some alternatives for less verbose error:

Start by reproducing the diagnostic with the Haxe example in the issue and compare the reported range with the alternatives shown in the attached images. Trace the compiler's missing-return diagnostic and adjust its range so the error highlights a narrower, more useful location; done means the example reports the improved range.

Written by the indexing model from the issue text.