Failed patch could left source code partially changed

[mithenks]

Problem

When a patch failed to apply to the source code this could be left partially changed.

Description

If a patch modify more than a file it could happens that it successfully applies to the first n files and then fails when reaching the n+1 file. In this case there isn't any rollback and the n modified files are left edited.

Expected behaviour

If a patch fails to apply the target source code should be left unchanged.