libstagefright_writer_fuzzer : Bug Fix

Initialized 'trackMime' using FuzzedDataProvider

Test: ./libstagefright_writer_fuzzer clusterfuzz-testcase-minimized-libstagefright_writer_fuzzer-5675078924238848
Bug: 190994150

Change-Id: Ie0c85b6afd21077d1c317ed57607fb1dcfacfabc
2 files changed