error: non-void function 'handle' should return a value [-Wreturn-mismatch]

I noticed a bug in hxcpp code generation.

### Code
```haxe
package;

class Test {
static function main() {
trace(new TestHandler());
}
}

class TestHandler extends AbstractHandler {
public function handle():Void {
var keys = [];
if (keys.length == 0) {
return;
}
}
}

abstract class AbstractHandler {
public function new() {}

public abstract function handle():T;
}
```

### Exception
```ex
Error: ./src/TestHandler.cpp:40:15: error: non-void function 'handle' should return a value [-Wreturn-mismatch]
40 | HXDLIN( 13) return;
| ^
1 error generated
```

### Environment
hxcpp 4.3.96
haxe 4.3.6
MacOS