Fix :scroll-page with --bottom-navigate on QtWebEngine

There were two issues here:

- The comparison was backwards, causing scroller.at_bottom() to always return
  true.
- When zoomed in, jsret['px']['y'] can be a float, which means we can be
  slightly off when checking the difference - math.ceil() fixes that.

CHANGELOG.asciidoc

@@ -137,6 +137,7 @@ Fixed
   fixed.
 - Scrolling to an anchor in a background tab now works correctly, and javascript
   gets the correct window size for background tabs.
+- `:scroll-page` with `--bottom-navigate` now works correctly on QtWebEngine
 
 v0.10.1
 -------

qutebrowser/browser/webengine/webenginetab.py

@@ -20,6 +20,7 @@
 """Wrapper over a QWebEngineView."""
 
 import os
+import math
 import functools
 
 import sip
@@ -342,7 +343,7 @@ class WebEngineScroller(browsertab.AbstractScroller):
             else:
                 perc_y = min(100, round(100 / dy * jsret['px']['y']))
 
-            self._at_bottom = dy >= jsret['px']['y']
+            self._at_bottom = math.ceil(jsret['px']['y']) >= dy
             self._pos_perc = perc_x, perc_y
 
             self.perc_changed.emit(*self._pos_perc)

tests/end2end/features/scroll.feature

@@ -292,6 +292,13 @@ Feature: Scrolling
         And I run :scroll-page --bottom-navigate next 0 1
         Then data/hello2.txt should be loaded
 
+    Scenario: :scroll-page with --bottom-navigate when not at the bottom
+        When I run :scroll-px 0 10
+        And I wait until the scroll position changed
+        And I run :scroll-page --bottom-navigate next 0 1
+        Then the following tabs should be open:
+            - data/scroll/simple.html
+
     Scenario: :scroll-page with --top-navigate
         When I run :scroll-page --top-navigate prev 0 -1
         Then data/hello3.txt should be loaded