Fix initial IDs not starting with 1

[ramonski]

Description of the issue/feature this PR addresses

When the ID Server does not find the generated key in its storage, e.g. for Sample Conditions the key samplecondition, it tries to handle the case when the storage was flushed and searches for all objects starting with this prefix.

Unfortunately, the temporary generated ID of the current context is there included, e.g. samplecondition.2019-10-10.5905228809 and the sequence number returns 10 in that case.

PDB Excerpt from https://github.com/senaite/senaite.core/blob/master/bika/lims/idserver.py#L457:

(Pdb++) a
context = <SampleCondition at samplecondition.2019-10-10.5905228809>
config = {'prefix': 'samplecondition', 'form': 'samplecondition-{seq}', 'sequence_type': 'generated'}
variables = {'seq': 0, 'parent': <SampleConditions at /senaitelims/bika_setup/bika_sampleconditions>, 'portal_type': 'SampleCondition', 'context': <SampleCondition at /senaitelims/bika_setup/bika_sampleconditions/samplecondition.2019-10-10.5905228809>, 'year': '19', 'alpha': AAA000, 'id': 'samplecondition.2019-10-10.5905228809'}
kw = {}
(Pdb++) context.id
'samplecondition.2019-10-10.5905228809'
(Pdb++) existing
['samplecondition.2019-10-10.5905228809']

Current behavior before PR

Initial IDs started with the sequence 11

Desired behavior after PR is merged

Initial IDs start with the sequence 1

--
I confirm I have tested this PR thoroughly and coded it according to PEP8
and Plone's Python styleguide standards.