Odd number of elements in hash error is no data_attributes param

[drn05r]

The following error messages occur when generating abstracts for items that have have a dimension badge box:

Odd number of elements in hash assignment at (eval 109) line 47.
Use of uninitialized value $attrs[4] in list assignment at (eval 109) line 47.

This is due to the following line:

dimensions-badge/lib/plugins/EPrints/Plugin/Screen/EPrint/Box/DimensionsBadge.pm

Line 97 in 51da0c8

(defined $self->param( 'data_attributes' ) ? %{$self->param( 'data_attributes' )} : undef ),

Rather than using undef if the a data_attributes param is undefined, () (i.e. an empty hash) should be used to ensure there is an even number of elements.