Check for EVP_Digest failure.

EVP_Digest can fail on malloc failure. May as well tidy that. Also make that
humongous comment less verbose.

Change-Id: I0ba74b901a5ac68711b9ed268b4202dc19242909
Reviewed-on: https://boringssl-review.googlesource.com/3331
Reviewed-by: Adam Langley <agl@google.com>
1 file changed