Do not include image header in decompressed size

Could cause a buffer overflow since we told LZ4 to decompress more
bytes than necessary.

Bug: 27561308

(cherry picked from commit 324eb2c6b049f1677133f0b708730e904c5e73ab)

Change-Id: I524c03b8f0e8a84814dbd8678285184e9d4da9f1
1 file changed