[Bug] inject fails silently when after or before match nothing

[c-vetter]

When after or before fail to match, the current behaviors are both surprising and different from each other:

• after injects at the start of the file
• before seems to do nothing

Both cases are logged as inject giving the impression that all is well. These behaviors are problematic because in the before-case important code may go missing, and in the after-case the resulting file may be broken.

Both should actually leave the file alone and log as skipped so the developer is immediately informed instead of trying to run this potentially broken state in the assumption that the generator worked as expected.