[VTS 2.3] Add length check before reading blob

Adding a length check prevents the read() from
reading outside the bounds and prevents OOB crash.

Test: atest VtsHalGraphicsComposerV2_3TargetTest && atest VtsHalGraphicsComposerV2_4TargetTest
BUG: 252764300
Change-Id: I6231e340a925127f9c32ccb76768286f7292df58