barcodedecode() did not always return barcode

barcodedecode() did not always return barcode

This patch amends the function to return barcode, in particular when
filter is not defined.  It also adds an optional 2nd argument to
allow the filter to be specified by caller, enabling testing.

Non-DB-dependent test script included.  Note: T-prefix style
barcode filter is not documented, and drops the first nonzero
digit after the T.  This seems mistaken, but is not corrected here
to avoid any surprises.

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>