xe: reduction: fixup exceptions on zero dims

[Simonsays095]

Fixes MFDNN-13039. Reduction gtests were enabled on the GPU in #2243, which revealed floating point exceptions when dividing by zero:

$ ctest -R test_reduction_gpu
Test project oneDNN/build
    Start 209: test_reduction_gpu
1/1 Test #209: test_reduction_gpu ...............***Exception: Numerical  0.31 sec

0% tests passed, 1 tests failed out of 1

Total Test time (real) =   0.32 sec

The following tests FAILED:
        209 - test_reduction_gpu (NUMERICAL)
Errors while running CTest

These errors are fixed by adding appropriate short-circuit checks to skip most logic (and execution) when a zero-dim is present.

[Simonsays095]

make test
disable test_device_cpu
enable test_device_gpu