Indexing errors will be reported even when index result is empty
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In the future, NumPy will raise an IndexError when an
integer array index contains out of bound values even if a non-indexed
dimension is of length 0. This will now emit a DeprecationWarning.
This can happen when the array is previously empty, or an empty
slice is involved::

    arr1 = np.zeros((5, 0))
    arr1[[20]]
    arr2 = np.zeros((5, 5))
    arr2[[20], :0]

Previously the non-empty index ``[20]`` was not checked for correctness.
It will now be checked causing a deprecation warning which will be turned
into an error. This also applies to assignments.