... which kicks in if SvxNumberFormatShell::FindEntry() determined
a format index of NUMBERFORMAT_ENTRY_NEW_CURRENCY instead of a
real existing index.

Regression from

    commit e607f1da
    CommitDate: Thu Oct 4 15:02:13 2018 +0200

        Select the current format if multiple instead of first matching format code

The old (now removed as unused)
SvxNumberFormatShell::GetListPos4Entry(const OUString&)
used before took care of that, add the functionality back but
combine into the existing GetListPos4Entry() function, the
additional FindEntry() call wasn't necessary anyway because it was
just called before in the caller.

The actual crash happened elsewhere in
SvNumberFormatter::GenerateFormat() because no format exists for
the then determined entry, which should be changed independently
to prevent such abuses.

Change-Id: Id42efa152693119fbde82b234f367679f818cfab
Reviewed-on: https://gerrit.libreoffice.org/66472Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins