[TF2XLA] In Resampler correctly handle out of boundary samples by returning 0

for the backward pass.

Note out of boundary here means outside of (-1, image_size) index, instead of
(0, image_size -1). As a result the images will be padded with 0 before
gathering / scattering operation is performed, then sliced back to obtain the
actual results.

PiperOrigin-RevId: 225278400