gsl_histogram*_clone should fail silently

[Achim Gaedke <Achim dot Gaedke at uni-koeln dot de>]

Hi!

If I try to clone an uninitialized histogram, the error handler is called twice.
The first time it is called by gsl_histogram*_calloc_range, then it is called
again from gsl_histogram*_clone, but with an irritating error message "failed to
allocate space for histogram struct".

The default error handler did not return, but often it is better to handle such
an error instead of aborting. With the appended patch, there is only one error
message: "histogram xrange not in increasing order".

Yours, Achim

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