Fixed handling empty zip file uploads

fix https://linear.app/tryghost/issue/SLO-102/end-of-central-directory-record-signature-not-found-an-unexpected

- previously, uploading an empty zip would result in a HTTP 500 error
  because yauzl would error and we'd bubble that up as an
  InternalServerError
- now, we catch the specific error message and return a more user
  friendly error
- also includes tests and sample zip file

ghost/core/core/server/data/importer/import-manager.js

@@ -235,6 +235,11 @@ class ImportManager {
                     help: tpl(messages.invalidZipFileNameEncodingHelp),
                     code: 'INVALID_ZIP_FILE_NAME_ENCODING'
                 });
+            } else if (err.message.includes('end of central directory record signature not found')) { // This comes from Yauzl when the zip is invalid
+                throw new errors.UnsupportedMediaTypeError({
+                    message: tpl(messages.invalidZipFileNameEncoding),
+                    code: 'INVALID_ZIP_FILE'
+                });
             }
             throw err;
         }

ghost/core/test/e2e-api/admin/db.test.js

@@ -103,4 +103,14 @@ describe('DB API', function () {
             }]
         });
     });
+
+    it('Handles invalid zip file uploads', async function () {
+        const res = await request.post(localUtils.API.getApiQuery('db/'))
+            .set('Origin', config.get('url'))
+            .attach('importfile', 'test/utils/fixtures/import/zips/empty.zip')
+            .expect('Content-Type', /json/)
+            .expect(415);
+
+        res.body.errors[0].message.should.eql('The uploaded zip could not be read');
+    });
 });