Fix double free on commit database migration

src/Cache.cpp

@@ -1727,12 +1727,14 @@ Cache::runMigrations()
                auto txn     = lmdb::txn::begin(env_, nullptr);
                auto mainDb  = lmdb::dbi::open(txn);
                auto dbNames = lmdb::cursor::open(txn, mainDb);
+               bool doCommit = false;
 
                std::string_view dbName;
                while (dbNames.get(dbName, MDB_NEXT)) {
                    if (!dbName.starts_with("olm_sessions.v2/"))
                        continue;
 
+                   doCommit = true;
                    auto curveKey = dbName;
                    curveKey.remove_prefix(std::string_view("olm_sessions.v2/").size());
 
@@ -1750,7 +1752,7 @@ Cache::runMigrations()
                    oldDb.drop(txn, true);
                }
 
-               txn.commit();
+               if (doCommit) txn.commit();
            } catch (const lmdb::error &e) {
                nhlog::db()->critical("Failed to convert olm sessions database in migration! {}",
                                      e.what());