PNG images are not supported in custom environments

[cvan]

Hardware

Any

Steps to Reproduce

1. In FxR, turn On the setting, Settings > Developer Options > Enable Environment Override.

2. Upload skybox images as .png (instead of .jpg) to the /sdcard/Android/data/org.mozilla.vrbrowser/files/skybox directory.

   FXR_SKYBOX_DIRECTORY=~/Downloads/skybox/ && \
           adb shell rm -rf /sdcard/Android/data/org.mozilla.vrbrowser/files/skybox && \                       
           adb push $FXR_SKYBOX_DIRECTORY /sdcard/Android/data/org.mozilla.vrbrowser/files/skybox && \
           adb shell ls /sdcard/Android/data/org.mozilla.vrbrowser/files/skybox
   

3. Relaunch FxR and notice the custom environment is not rendered (void/black).

Current Behavior

Custom environments are not rendered if the images are both JPEG files and end with the .jpg extension.

It looks like the custom-skybox code is hardcoded for .jpg files. (I tried renaming the .png files to .jpg, but that did not work either.)

When I converted the .png files to .jpg files, the environment rendered properly.

Expected Behavior

Custom environments can be rendered if they are in a valid Android-supported image format (that is, not only if the images end with the .jpg extension).