libcamera2ndk_vendor: Fix potential use after free of camera_metadata_t

Bug: 131566406

Test: Use libcamera2ndk_vendor multiple times without seeing logs /
      assertions indicating null metadata / corrupted metadata in
      allocateACaptureRequest.

Change-Id: I2154a83bb97a4dd945f15328769b811e9485a0ac
Signed-off-by: Jayant Chowdhary <jchowdhary@google.com>