mpeg4_enc_fuzzer: Bug Fix

Replaced stack allocation with heap allocation

Test: ./mpeg4_enc_fuzzer clusterfuzz-testcase-minimized-mpeg4_enc_fuzzer-5379218936561664
Bug: 172714629

Change-Id: I627c448d15a5de56a5a313bbeffb64c4dc5d1fae
1 file changed