Check mDataPos to see if the Parcel needs to grow

Flag: EXEMPT bug fix
Ignore-AOSP-First: security fix
Test: atest binderUnitTest
Bug: 399155883
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f0b1c904a607f4dea4f35e3e9bc53e25f059f50e)
Merged-In: I38b755ca3381cfca3300292873f763823fbf169b
Change-Id: I38b755ca3381cfca3300292873f763823fbf169b