Bug 19328: Internal server error because of missing currency

Bug 19328: Internal server error because of missing currency

This patch fixes internal server errors because of missing active currency
in files aqbudgetperiods.pl, aqbudgets.pl and aqplan.pl.

To reproduce:
- Make sure that no active currency is defined. You can undefine the active
  currency in Administration->Currencies and exchange rates
- Try to go to Administration->Budgets and Admistration->Funds
Result: Internal server error

To test:
- Apply patch
- Restart plack
- Try to reproduce issue, it should no longer occur. There should be a
  yellow message box "No active currency is defined"
- From Administration-> Budgets administration try to edit a fund and go to
  "Planning". Verify that the message box appears here as well.

Signed-off-by: David Bourgault <david.bourgault@inlibro.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>