XAPK: XAPKInstallUtils: Use safe calls on nullable parentFile

- Compile-time warnings observed

w: /builds/e/apps/apps/app/src/main/java/foundation/e/apps/XAPK/XApkInstallUtils.kt: (144, 22): Unsafe use of a nullable receiver of type File?
w: /builds/e/apps/apps/app/src/main/java/foundation/e/apps/XAPK/XApkInstallUtils.kt: (145, 21): Unsafe use of a nullable receiver of type File?

Signed-off-by: Aayush Gupta <theimpulson@e.email>