BUG: Fix concatenation when the output is "S" or "U"

Previously, the dtype was used, this now assumes that we want to
cast to a string of (unknown) length.  This is a simplified version
of what happens in `np.array()` or `arr.astype()` (it does never
inspect the values, e.g. for object casts).

This is more complex as I would like, and with the refactor of
ResultType and similar can be cleaned up a bit more hopefully.

Note that currently, object to "S" or "U" casts simply return
length 64 strings, but with the new version, this will be an error
(although the error message probably needs improvement).
This is a behaviour inherited from other places however.

0 files changed, 0 insertions, 0 deletions