mport verify can compare stale checksum data after hashing failures

mport is the MidnightBSD Package Manager. Prior to 2.7.8, mport_verify_package() in libmport/verify.c could continue after MD5File() or SHA256_File() failed and compare an expected checksum with stale data in the hash buffer rather than a newly computed digest. An attacker able to influence an installed file or the conditions that make hashing fail could receive a misleading integrity result or hide a checksum failure. This issue is fixed in version 2.7.8.