libinput: avoid null segmentation fault

readCString may return nullptr, and it's deprecated
and old anyway.

Please also consider converting this code to use
AIDL-defined parcelables. go/aidl-it!

Bug: 301519740
Test: w/ fuzzer
Change-Id: I76050c3b7fe40964fd751e678688d2e1d97b9479
1 file changed