Catch exceptions when trying to read HTTP body in logs

Fixes https://sentry.io/organizations/coreos/issues/627586398/events/9ea9873f11e6456abc58f5de10951e44/?project=52148

app.py

@@ -11,6 +11,7 @@ from flask_login import LoginManager
 from flask_mail import Mail
 from flask_principal import Principal
 from jwkest.jwk import RSAKey
+from werkzeug.exceptions import HTTPException
 
 import features
 
@@ -143,7 +144,11 @@ FILTERED_VALUES = [
 
 @app.after_request
 def _request_end(resp):
-  jsonbody = request.get_json(force=True, silent=True)
+  try:
+    jsonbody = request.get_json(force=True, silent=True)
+  except HTTPException:
+    jsonbody = None
+
   values = request.values.to_dict()
 
   if jsonbody and not isinstance(jsonbody, dict):