Fix the compound key constructors for AccountAgreement, AccountGroupMember

A compound key must allocate its referenced subkeys during its no-arg
constructor.  This is assumed to be true by gwtorm as it unpacks the
entity from a java.sql.ResultSet and creates it.

Signed-off-by: Shawn O. Pearce <sop@google.com>

webapp/src/com/google/gerrit/client/reviewdb/AccountAgreement.java

@@ -32,6 +32,8 @@ public final class AccountAgreement {
     protected ContributorAgreement.Id claId;
 
     protected Key() {
+      accountId = new Account.Id();
+      claId = new ContributorAgreement.Id();
     }
 
     public Key(final Account.Id account, final ContributorAgreement.Id cla) {

webapp/src/com/google/gerrit/client/reviewdb/AccountGroupMember.java

@@ -26,6 +26,8 @@ public final class AccountGroupMember {
     protected AccountGroup.Id groupId;
 
     protected Key() {
+      accountId = new Account.Id();
+      groupId = new AccountGroup.Id();
     }
 
     public Key(final Account.Id a, final AccountGroup.Id g) {