XLA patch, flip select true/false in mask

enables:
```
const bool pad_value_is_zero =
pad_value->IsConstant() && pad_value->literal().IsZero({});
```

to become true

Start by locating the XLA mask handling code associated with the pad_value_is_zero condition shown in the issue. Compare how the mask currently selects true and false, then determine the intended behavior for the condition becoming true. Done means the XLA patch applies the requested selection change and the relevant existing checks pass.

Written by the indexing model from the issue text.