[macos] Moving map to a screen with a different pixel density crashes

[JesseCrocker]

Platform: MacOS
Mapbox SDK version: Master @ 164d156
Hardware: iMac (Retina 5K, 27-inch, Late 2014), with 2 additional non-retina screens

Steps to trigger behavior

1. Run macosapp target on a retina screen
2. Move window to a non-retina screen

Expected behavior

Map stays functional

Actual behavior

Application crashes with error. libc++abi.dylib: terminating with uncaught exception of type mbgl::gl::Error: glUseProgram(value): Error GL_INVALID_VALUE at /Users/jesse/projects/mapbox-gl-native/src/mbgl/gl/value.cpp:223

[jfirebaugh]

Duplicate of #6654.