Added protection against "too many SQL variables" for SQLite3

no issue

- discovered while testing
- SQLite3 has a restriction that you cannot query more than 999 SQL variables (e.g. fetch all tag relations for all posts)
- if you have more than 999 posts in your database, Ghost wasn't able to finish the bootstrap
  - the url service tried to fetch all posts & relations, but could not complete, because SQlite3 has thrown
    -> "too many SQL variables"
- i have added a recursive query strategy only for SQLite3
  - use offset/limit

core/server/models/base/index.js

@@ -1071,6 +1071,14 @@ ghostBookshelf.Model = ghostBookshelf.Model.extend({
 
             let query = ghostBookshelf.knex(tableNames[modelName]);
 
+            if (options.offset) {
+                query.offset(options.offset);
+            }
+
+            if (options.limit) {
+                query.limit(options.limit);
+            }
+
             // exclude fields if enabled
             if (reducedFields) {
                 const toSelect = _.keys(schema.tables[tableNames[modelName]]);
@@ -1090,6 +1098,11 @@ ghostBookshelf.Model = ghostBookshelf.Model.extend({
             return query.then((objects) => {
                 debug('fetched', modelName, filter);
 
+                if (!objects.length) {
+                    debug('No more entries found');
+                    return Promise.resolve([]);
+                }
+
                 let props = {};
 
                 if (!withRelated) {

core/server/services/url/Resources.js

@@ -2,6 +2,7 @@ const debug = require('ghost-ignition').debug('services:url:resources'),
     Promise = require('bluebird'),
     _ = require('lodash'),
     Resource = require('./Resource'),
+    config = require('../../config'),
     models = require('../../models'),
     common = require('../../lib/common');
 
@@ -132,16 +133,30 @@ class Resources {
             });
     }
 
-    _fetch(resourceConfig) {
+    _fetch(resourceConfig, options = {offset: 0, limit: 999}) {
         debug('_fetch', resourceConfig.type, resourceConfig.modelOptions);
 
-        return models.Base.Model.raw_knex.fetchAll(resourceConfig.modelOptions)
+        let modelOptions = _.cloneDeep(resourceConfig.modelOptions);
+        const isSQLite = config.get('database:client') === 'sqlite3';
+
+        // CASE: prevent "too many SQL variables" error on SQLite3
+        if (isSQLite) {
+            modelOptions.offset = options.offset;
+            modelOptions.limit = options.limit;
+        }
+
+        return models.Base.Model.raw_knex.fetchAll(modelOptions)
             .then((objects) => {
                 debug('fetched', resourceConfig.type, objects.length);
 
                 _.each(objects, (object) => {
                     this.data[resourceConfig.type].push(new Resource(resourceConfig.type, object));
                 });
+
+                if (objects.length && isSQLite) {
+                    options.offset = (options.offset + 1) * options.limit;
+                    return this._fetch(resourceConfig, {offset: options.offset, limit: options.limit});
+                }
             });
     }