Check if return value from `LZ4_decompress_safe()` is negative.

`LZ4_decompress_safe()` returns an `int`, which was previously cast
to `size_t` without checking for possible negative values. This hides
possible errors (they hit the following assertion that decompressed size
equals image size). Instead, fail to decompress the image if return
value is negative.

Bug: 242914915
Test: art/test.py --host
Change-Id: I0e330bbbd55ccbef124230b6b50915ea8d009b03
3 files changed