create unique index for contact prekeys (to allow using REPLACE)

app/sql.js

@@ -447,6 +447,11 @@ async function updateToSchemaVersion6(currentVersion, instance) {
     );`
   );
 
+  await instance.run(`CREATE UNIQUE INDEX contact_prekey_identity_key_string_keyid ON contactPreKeys (
+    identityKeyString,
+    keyId
+  );`);
+
   await instance.run(
     `CREATE TABLE contactSignedPreKeys(
       id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
@@ -456,6 +461,11 @@ async function updateToSchemaVersion6(currentVersion, instance) {
     );`
   );
 
+  await instance.run(`CREATE UNIQUE INDEX contact_signed_prekey_identity_key_string_keyid ON contactSignedPreKeys (
+    identityKeyString,
+    keyId
+  );`);
+
   await instance.run('PRAGMA schema_version = 6;');
   await instance.run('COMMIT TRANSACTION;');
   console.log('updateToSchemaVersion6: success!');