Layer.hx - Cannot inline a not final return

Sometimes (I can not understand exactly when), I got the error "Cannot inline a not final return" on the following lines of code:

```haxe
public inline function isCoordValid(cx,cy) {
	return cx>=0 && cx<cWid && cy>=0 && cy<cHei;
}
```

Removing the inlining of the condition fixes the issue.

**API version**: 1.5.3-rc1