fix: check PR is closed when finding blocking PR

Closes #2391

lib/workers/branch/check-existing.js

@@ -13,6 +13,12 @@ async function prAlreadyExisted(config) {
   const pr = await platform.findPr(config.branchName, config.prTitle, '!open');
   if (pr) {
     logger.debug('Found closed PR with current title');
+    const prDetails = await platform.getPr(pr.number);
+    // istanbul ignore if
+    if (prDetails.state === 'open') {
+      logger.debug('PR reopened');
+      throw new Error('repository-changed');
+    }
     return pr;
   }
   logger.debug('prAlreadyExisted=false');

test/workers/branch/check-existing.spec.js

@@ -26,6 +26,7 @@ describe('workers/branch/check-existing', () => {
     });
     it('returns true if first check hits', async () => {
       platform.findPr.mockReturnValueOnce({ number: 12 });
+      platform.getPr.mockReturnValueOnce({ number: 12, state: 'closed' });
       expect(await prAlreadyExisted(config)).toEqual({ number: 12 });
       expect(platform.findPr.mock.calls.length).toBe(1);
     });