Check for null system device

Check for null device in gsi service and return invalid fd
when device is null. Adding checks for invalid fd.

Test: atest vts_gsi_boot_test
Test: m gsi_service_fuzzer && adb sync data && adb shell /data/fuzz/x86_64/gsi_service_fuzzer/gsi_service_fuzzer -runs=10000
Bug: 309822660
Change-Id: Iaea180a0c1dac77bdf99c432c795633ceb849bd1
2 files changed