Fix crash with secondary dex files on low RAM devices.

Before a secondary dex files gets dexopted, we create a vdex-only file.
Vdex-only files don't have dexlayout sections.

Test: 692-vdex-secondary-loader
Bug: 184262593
Change-Id: I020f82943bb64060bce280771e40dcd01a6d4d40
3 files changed