Map re-requests over-zoomed tiles causing rendering flicker [0.40.0]

[ryanbaumann]

mapbox-gl-js version: 0.40.0

Steps to Trigger Behavior

1. Load Mapbox-Streets tileset on GL JS examples page at https://www.mapbox.com/mapbox-gl-js/examples/
2. Zoom into new york at zoom 16.
3. Double-click to zoom into zoom 17+

Expected Behavior

Map over-zooms on existing loaded tiles past a tileset max zoom. User experience is a smooth zoom without rendering flicker past a vector tileset max zoom.

Actual Behavior

Map re-requests tile resources past a vector tileset max zoom, causing a re-render and flicker.

This PR from the previous release may be the source of the bug -> b05ecaa

cc @mollymerp