deploy:deploy will try to deploy a nonexistent attached file (and succeed, depending on the repository)

If a nonexistent file is attached to a project using build-helper-maven-plugin, deploy:deploy will attempt to deploy it (and, depending on the repository manager, possibly create a zero-length artifact in the process).

Detail: We have a legacy build process that generates RPMs using .spec files and command-line tools, then attaches the artifacts to the build using build-helper-maven-plugin. Occasionally the .spec file version gets out of date; the RPM is still generated successfully, so build-helper-maven-plugin attaches what it thinks will be the path to the generated file (but isn't, because the version is wrong). When maven-deploy-plugin:deploy runs, it tries to upload the nonexistent file to Nexus, which creates a zero-length artifact. (This eventually causes Nexus's yum plugin to fail, as the underlying createrepo process can't handle the zero-length RPM file is invalid.)

The patch will no longer deploy the nonexistent file, printing a warning when this happens instead.