Bug 22222: Don't send empty params to mana service

Bug 22222: Don't send empty params to mana service

Test plan:
0) Do not apply the patch
1) Go to serials > Search on Mana
2) Insert some value into the form
3) Submit -> you get many (3000+) results
4) Apply the patch and restart_all
5) Repeat, now, you get only the subscription matching your query

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Alex Arnaud <alex.arnaud@biblibre.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>