GMTED being used erroneously at high zoom levels

[DaMatrix]

According to https://github.com/tilezen/joerd/blob/master/docs/data-sources.md#what-is-sourced-at-what-zooms, GMTED data should only be being used for land data between zooms 4-6. However, when testing bathymetry at 0,0, I noticed the following:

• Zoom 10 (working)

  
  

• Zoom 11 (broken)

  
  

For some reason, zoom levels 11+ are using GMTED data in the ocean near 0,0, instead of ETOPO1 as documented. Tested manually on all zoom levels 11-15.