Handle failing javascript in webelem.rect_on_view

Fixes #1641.

CHANGELOG.asciidoc

@@ -25,6 +25,11 @@ Changed
 - `:bookmark-load` now has a `--delete` flag which deletes the bookmark after
   loading it.
 
+Fixed
+-----
+
+- Fixed crash when using hints with JS disabled in some rare circumstances.
+
 v0.8.1
 ------
 

qutebrowser/browser/webkit/webelem.py

@@ -367,6 +367,12 @@ class WebElementWrapper(collections.abc.MutableMapping):
     def _rect_on_view_js(self, adjust_zoom):
         """Javascript implementation for rect_on_view."""
         rects = self._elem.evaluateJavaScript("this.getClientRects()")
+        if rects is None:
+            # Depending on unknown circumstances, this might not work with JS
+            # disabled in QWebSettings:
+            # https://github.com/The-Compiler/qutebrowser/issues/1641
+            return None
+
         text = utils.compact_text(self._elem.toOuterXml(), 500)
         log.hints.vdebug("Client rectangles of element '{}': {}".format(
             text, rects))