Fix dictionary force reloading clevel selection

[senhuang42]

As title - reloading the dictionary with ZSTD_dictForceLoad was basically broken because we would always choose the default compression level since initLocalDict() always sets a cdict. Now, we only override cctx clevel with cdict's clevel if the cctx had the cdict to begin with.

results.csv updated accordingly.

[senhuang42]

Investigating the surprising non determinism failures... these are locally reproducible too. I wonder if this is exposing an existing bug or is the cause itself.

Edit: Seems to be because subsequent calls of compressStream2() that have a localDict would appear to have a dedicated cdict, and therefore we'd end up taking that cdict's level when we shouldn't. So, we should check that there is no localDict.cdict as well.

[terrelln]

@senhuang42 I think this is correct, but it is really confusing to have moved this above ZSTD_initLocalDict(). When ZSTD_initLocalDict() is creates a cdict, this will never run, because necessarily cctx->cdict == nullptr in that case. Since ZSTD_CCtx_loadDictionary() first calls ZSTD_clearAllDicts().

I believe that leaving this line in the original location (L5170), with the additional !cctx->localDict.cdict check will behave identically, but is much clearer.