Fixed unhandled promise rejection in Redis adapter _get timeout path

ghost/core/core/server/adapters/lib/redis/AdapterCacheRedis.js

@@ -181,6 +181,9 @@ class AdapterCacheRedis extends BaseCacheAdapter {
                 this.cache.get(key).then((result) => {
                     clearTimeout(timer);
                     resolve(result);
+                }).catch(() => {
+                    clearTimeout(timer);
+                    resolve(null);
                 });
             });
         }

ghost/core/test/unit/server/adapters/lib/redis/adapter-cache-redis.test.js

@@ -60,6 +60,24 @@ describe('Adapter Cache Redis', function () {
             assert.equal(value, 'value from cache');
         });
 
+        it('returns null if the cache get rejects and getTimeoutMilliseconds is set', async function () {
+            const redisCacheInstanceStub = {
+                get: sinon.stub().rejects(new Error('Stream isn\'t writeable and enableOfflineQueue options is false')),
+                store: {
+                    getClient: sinon.stub().returns({
+                        on: sinon.stub()
+                    })
+                }
+            };
+            const cache = new RedisCache({
+                cache: redisCacheInstanceStub,
+                getTimeoutMilliseconds: 100
+            });
+
+            const value = await cache.get('key');
+            assert.equal(value, null);
+        });
+
         it('returns null if getTimeoutMilliseconds is exceeded', async function () {
             const redisCacheInstanceStub = {
                 get: sinon.stub().callsFake(async () => {