Android fill value issues in texture mode

[Shane98c]

Testing on a pixel 6a with latest chrome (also reproducible on firefox for android):

• fill value of 9.969209968386869e36 is not being discarded and instead rendered as a very large number
• https://github.com/carbonplan/maps/blob/b9782db090db4f8383ba5944cae36ec5674c973b/src/shaders.js#L152-L154
• based on debugging it looks like the fill value is being treated as at least an order of mag larger number than it is, we were able to extract the expected fill value using the region picker, so the issue appears to be in the fragment shader.
• Reproduced in prototype-maps https://github.com/carbonplan/prototype-maps (issue initially noticed in https://github.com/carbonplan/oae-web).
• Also tested with toggling forest-carbon viewer to use 'texture' and saw initial flash of the issue, soon corrected by

yellow areas are the fillValue areas, continent interiors are manually filled with zeros in the below screenshot.