Build button is disabled and a warning message appears for linear colorspace if OpenGLS2 is included in the Graphics API list and is not the active graphics API

Steps to reproduce:
1. Launch the editor.
2. Create a 2D/3D project.
3. Go to -> File-> Build Settings.
4. Switch platform to Android/iOS.
5. Proceed to player settings.
6. Change the colorspace to 'Linear'.
7. Add 'Open GLES2' in the Graphics API list.
8. Observe that the warning message regarding 'Open GLES2 appears.
9. Keep Vulcan/OpenGLES3 on the top of the list.
10. Observe that the warning doesn't go away and the build button remains disabled.

Reproducible on: 2018.1.0f1,

Environment
Windows and Mac