Bug 11663: fix display of holding tab in Bootstap OPAC when opacbookbag syspref is...

Bug 11663: fix display of holding tab in Bootstap OPAC when opacbookbag syspref is disabled

Bootstap theme opac holding tab is improperly displayed when opacbookbag
syspref is disabled, and virtualshelf is enabled. This is due to the
fact that in this situation basket.js is loaded (for virtual shelves),
but some JS variables are not defined in template since opacbookbag is
disabled.

To reproduce this bug:

- Choose bootstrap OPAC theme
- Enable virtualsheves syspref
- Disable opacbookbag syspref
- Open a biblio record in OPAC detail page
- You will observe that items holding tabs are not displayed as tabs but
  as a bulleted list

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes QA script and all tests.
Confirmed display problem exists without the patch and is solved by it.
Ideally we would avoid having the cart messages in the template when
the feature is deactivated, but this is ok for now.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>