[BioRuby] Detect error from Bio::Fetch

[Yen-Ju Chen]

This is the script I run:

require 'bio'
serv = Bio::Fetch.new()
entry = serv.fetch('swissprot', 'not_existing_id')
swissprot = Bio::SwissProt.new(entry)
p swissprot.entry_name # <== Error raises here

The problem is that Bio.Fetch does not raise an exception or something
else to notify that it cannot find the entry in database. An error
shows up only at 'swissprot.entry_name'. It would be nice to detect
the error early on, either in Bio::Fetch.fetch() or
Bio::SwissProt.new().

Yen-Ju