Prefer ANDROID_NDK_HOME over the ANDROID_HOME ndk-bundle location

[andydotxyz]

tidy order of operations to prefer more specific environment variable.

Fixes #2899

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

[coveralls]

Coverage remained the same at 61.669% when pulling 3bc3766 on andydotxyz:fix/2899 into 96d8124 on fyne-io:develop.

[Jacalz]

Keep in mind that I don’t have an Android development environment set up. However, the code is short and readable while also making a lot of sense so I’ll approve it :)