Correct reporting of errors in MediaCrypto

Legacy error codes need to be converted into new Status values before
being reported. Decryption errors (that were negative) were changed to
absolute values. This caused their translation to new Status values to
fail.

b/35634335

Test: Verified with GtsExoPlayerTestCases. Some failures, but those
      are unrelated to this CL and will be addressed separately.

Change-Id: I995cac33cb2725d02b0f1a3922e522ce07a9d1be