Bug 30243: When branccode is required on OPAC suggestion page default to empty value

Bug 30243: When branccode is required on OPAC suggestion page default to empty value

To test:
1. Apply patch
2. Go the purchase suggestion page and see that branchcode defaults to the first option in the list.
3. Go to OPACSuggestionMandatoryFields and mark branchcode as required
4. BAck on the OPAC suggestion page notice that the branchcode defaults to an empty value
5. Try to submit the form without changing it, you cannot. You must choose a branch

Signed-off-by: shiyao <shiyao@inlibro.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>