Apply fix for vendor pull request #17: Support appending to empty archives
Apply fix for vendor pull request #17:
Support appending to empty archives

References:
  https://github.com/libarchive/libarchive/pull/17

Submitted by:	myself
Obtained from:	libarchive master branch on github

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase