Catch invalid XML in suggestion response

As reported in #593, the XML response body returned for search
suggestions can apparently contain invalid XML elements. This catches
the error and returns an empty suggestion list instead of erroring.

Fixes #593

app/request.py

@@ -229,9 +229,13 @@ class Request:
         if not response:
             return []
 
+        try:
             root = ET.fromstring(response)
             return [_.attrib['data'] for _ in
                     root.findall('.//suggestion/[@data]')]
+        except ET.ParseError:
+            # Malformed XML response
+            return []
 
     def send(self, base_url='', query='', attempt=0,
              force_mobile=False) -> Response: