Binary caching: fix buildcache list (multiple invocations) (#19848)
Binary caching: fix buildcache list (multiple invocations) (#19848)

When invoking "buildcache list" multiple times, the command was
reporting no specs in the cache the second time around. The
presence of an up-to-date index was causing the internal
representation to be left un-initialized.
iulian787/spack,LLNL/spack,LLNL/spack,iulian787/spack,LLNL/spack,iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack,LLNL/spack