Bug 9770: fix sorting of Dewey call numbers that contain prefixes

Bug 9770: fix sorting of Dewey call numbers that contain prefixes

C4::ClassSortRoutine::Dewey can pad the wrong part of a call number internally.

The subroutine get_class_sort_key tokenizes a call number string (splitting on
periods and whitespace) and counts the number of tokens that solely contain
digits.  If there is only one such digit group, a comment in the code states
that it will pad said digit group.  However, the bug is that the code assumes
said digit group is the first token, when this may not be the case.

In practice, this can cause poor sorting when used a call number is in the form
of PREFIX _space_ 3DIGITS.

To test:

[1] Create two item records whose class scheme is set to
    'ddc' (Dewey) and whose call numbers contain prefixes, e.g.,
    J DVD 700.1 ABC and J DVD 850 DEF.
[2] Use the inventory tool to produce a list of item items that include
    the two created in step 1.  Obsere that that items are sorted
    in the incorrect order, with "J DVD 850 DEF" coming before
    "J DVD 700.1 ABC".  Alternatively, run the following SQL
    to see the incorrect sort order:

    SELECT cn_sort, itemcallnumber
    FROM items
    WHERE itemcallnumber LIKE 'J DVD%'
    ORDER BY cn_sort;

[4] Apply this patch.
[5] Run misc/maintenance/touch_all_items.pl to force cn_sort to be
    recalculated.
[6] Repeat step 2 and verify that the call numbers are now sorted
    corrected.

Signed-off-by: Jason Etheridge <jason@esilibrary.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>