fdroid rewritemeta should not remove prebuild on error
Looks like we have a regression where prebuild= is not getting executed at all. In fact, it gets removed by `fdroid rewritemeta` completely.
Update: fdroidrewrite removes prebuild completely when its unterminated, e.g.
````
prebuild=true && \
````
I am not sure this is a regression, but it feels like it. Since I had the habit of running rewritemeta before actually building for a long time and iirc never run into this behaviour. I think a better solution would be to error or fixit by removing the last "&& \" if possible. Removing the whole prebuild might kill quite some work, if i havent made any backups or commited before.
issue