handle suspected source of errors

atime update on cache entries blocked calendar event creation for me once
seemingly due to an unhandled DOMException triggered by localForage.
This is the only place I expect it could have come from, but the error message wasn't very helpful
so I could be wrong

www/common/outer/cache-store.js

@@ -49,7 +49,10 @@ define([
                 }
                 cb(null, obj.c);
                 obj.t = +new Date();
-                cache.setItem(id, obj);
+                cache.setItem(id, obj, function (err) {
+                    if (!err) { return; }
+                    console.error(err);
+                });
             });
         });
     };
@@ -81,7 +84,10 @@ define([
                 }
                 cb(null, obj);
                 obj.t = +new Date();
-                cache.setItem(id, obj);
+                cache.setItem(id, obj, function (err) {
+                    if (!err) { return; }
+                    console.error(err);
+                });
             });
         });
     };