TimeZones.build doesn't rebuild compiled files upon failure

[omus]

While working on #471 I noticed at after I introduced the fix in #472 I couldn't use TimeZones.build("2024b") to re-build without first deleting the compiled/tzjf/v1/2024b scratch folder first:

julia> TimeZones.build("2024b")
ERROR: Cache remains empty after loading
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] reload!
   @ ~/.julia/dev/TimeZones/src/types/timezonecache.jl:40 [inlined]
 [3] _reload_tz_cache
   @ ~/.julia/dev/TimeZones/src/types/timezonecache.jl:73 [inlined]
 [4] build(version::String; force::Bool)
   @ TimeZones ~/.julia/dev/TimeZones/src/build.jl:16
 [5] build(version::String)
   @ TimeZones ~/.julia/dev/TimeZones/src/build.jl:11
 [6] top-level scope
   @ REPL[2]:1

Seems like we should check that the destination directory both exists and is not empty when skipping compilation.

[omus]

Was fixed by #474