message: Fixed issue with re-establishing connection if the backend is unexpectedly shutdown.
  (this also fixes some of the frontend integration tests)
diff: @@ -714,12 +714,12 @@ export class IModelDb extends IModel {
  public static find(iModelToken: IModelToken): IModelDb {
  // Logger.logTrace(loggingCategory, "Finding IModelDb", () => ({ iModelId: iModelToken.iModelId, changeSetId: iModelToken.changeSetId, key: iModelToken.key }));
  const briefcaseEntry = BriefcaseManager.findBriefcaseByToken(iModelToken);
  - if (!briefcaseEntry) {
  + if (!briefcaseEntry || !briefcaseEntry.iModelDb) {
  Logger.logError(loggingCategory, "IModelDb not found", () => ({ iModelId: iModelToken.iModelId, changeSetId: iModelToken.changeSetId, key: iModelToken.key }));
  throw new IModelNotFoundResponse();
  }
  // Logger.logTrace(loggingCategory, "Found IModelDb", () => ({ iModelId: iModelToken.iModelId, changeSetId: iModelToken.changeSetId, key: iModelToken.key }));
  - return briefcaseEntry.iModelDb!;
  + return briefcaseEntry.iModelDb;
  }
  /** Get the ClassMetaDataRegistry for this iModel. */
  