Comment 7 for bug 1571788

Further testing indicates that apport (or gdb) will sometimes retrace a report and yet there will not be a crash signature after retracing. This can happen if we are missing debug symbols or the crash had old package versions. However, there are also cases where the report does not have an UnreportableReason, is not missing debug symbols, has an original StacktraceAddressSignature and the retraced report has a StacktraceTop full of "?? ()". In those cases we should try retracing again and see what happens.