Raise a tailored error when calling "transaction.search" with empty "phids" constraint

Summary:
Ref T13164. See PHI725. For real "*.search" methods, parameters get validated and you get an error if you use an empty list as a constraint.

Since "transaction.search" isn't really a normal "*.search" method, it doesn't benefit from this. Just do the check manually for now.

Test Plan: Made `transaction.search` calls with no constraints (got results); a valid costraint (got fewer results); and an invalid empty constraint (got an exception).

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13164

Differential Revision: https://secure.phabricator.com/D19562

src/applications/transactions/conduit/TransactionSearchConduitAPIMethod.php

@@ -79,6 +79,14 @@ final class TransactionSearchConduitAPIMethod
       ));
 
     $with_phids = idx($constraints, 'phids');
+
+    if ($with_phids === array()) {
+      throw new Exception(
+        pht(
+          'Constraint "phids" to "transaction.search" requires nonempty list, '.
+          'empty list provided.'));
+    }
+
     if ($with_phids) {
       $xaction_query->withPHIDs($with_phids);
     }