Bug: replace_symbol_in_expr() fails if the expression contains NA

### What happened?

`replace_symbol_in_expr()` fails if the expression contains `NA`.

### Session Information

_No response_

### Reproducible Example

```
> replace_symbol_in_expr(expr(if_else(AVAL > 0, AVAL, NA)), !!expr(AVAL), !!expr(AVAL.join))
Error in if (expression[[i]] == target) { : 
  missing value where TRUE/FALSE needed
```