Check HIDL Discriminator for CSG Info

ART throws an exception if an unpopulated safe union element
is accessed at runtime, so instead we have to check the
hidl_discriminator to see whether the element is populated
before trying to access it (and thus we skip the null check).

Bug: 152486447
Test: atest testCellIdentityLte_1_5_CsgInfo \
        testCellIdentityWcdma_1_5_CsgInfo \
        testCellIdentityTdscdma_1_5_CsgInfo
Merged-In: I08dc0d2050a9f4d4b574178e1c68a23d015768e4
Change-Id: I08dc0d2050a9f4d4b574178e1c68a23d015768e4
(cherry picked from commit f85a2e9220cb523dcb8c05d04a7bcb8b2cfcaf6d)

(cherry picked from commit 8f19e4f21f858ef31075f6163b4ffff43a4420c9)

CRs-Fixed: 2726148
Change-Id: I2ef5510c5fcfa7093f838a3cdcc44e5609b85a9d
3 files changed