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();
             }
         }
     }

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/model/KeySignature.java

@@ -22,6 +22,6 @@ public abstract class KeySignature implements KeySignaturesModel {
     }
 
     public static KeySignature create(long masterKeyId, long certId) {
-        return null;
+        return new AutoValue_KeySignature(masterKeyId, certId);
     }
 }