Fix grid bug if "current page" becomes invalid

sometimes it was possible to fall outside the valid page range, in which
case grid would stop showing results!

tailbone/grids/core.py

@@ -698,11 +698,11 @@ class Grid(object):
         page = self.request.GET.get('page')
         if page is not None:
             if page.isdigit():
-                settings['page'] = page
+                settings['page'] = int(page)
         else:
             page = self.request.session.get('grid.{}.page'.format(self.key))
             if page is not None:
-                settings['page'] = page
+                settings['page'] = int(page)
 
     def persist_settings(self, settings, to='session'):
         """
@@ -775,12 +775,26 @@ class Grid(object):
         Paginate the given data set according to current settings, and return
         the result.
         """
-        if self.model_class:
+        if not self.model_class:
+            return data
+
+        # we of course assume our current page is correct, at first
+        pager = self.make_pager(data)
+
+        # if pager has detected that our current page is outside the valid
+        # range, we must re-orient ourself around the "new" (valid) page
+        if pager.page != self.page:
+            self.page = pager.page
+            self.request.session['grid.{}.page'.format(self.key)] = self.page
+            pager = self.make_pager(data)
+
+        return pager
+
+    def make_pager(self, data):
         return SqlalchemyOrmPage(data,
                                  items_per_page=self.pagesize,
                                  page=self.page,
                                  url_maker=URLMaker(self.request))
-        return data
 
     def make_visible_data(self):
         """