fix insertion of data into KeySignature table

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/daos/DatabaseBatchInteractor.java

@@ -57,6 +57,8 @@ public class DatabaseBatchInteractor {
             } else if (op.keySignature != null) {
                 op.keySignature.bindTo(insertKeySignerStatement);
                 insertKeySignerStatement.executeInsert();
+            } else {
+                throw new IllegalStateException();
             }
         }
     }