Fix buffer overrun in ZSTD_loadDictEntropyStats()
The table log set by `FSE_readNCount()` was not checked in
`ZSTD_loadDictEntropyStats()`. This caused `FSE_buildCTable()`
to stack/heap overflow in a few places.
The benchmarks look good, there is no obvious compression performance regression:
> ./zstds/zstd.opt.0 -i10 -b1 -e10 ~/bench/silesia.tar
1#silesia.tar : 211988480 -> 73656930 (2.878), 271.6 MB/s , 716.8 MB/s
2#silesia.tar : 211988480 -> 70162842 (3.021), 204.8 MB/s , 671.1 MB/s
3#silesia.tar : 211988480 -> 66997986 (3.164), 156.8 MB/s , 658.6 MB/s
4#silesia.tar : 211988480 -> 66002591 (3.212), 136.4 MB/s , 665.3 MB/s
5#silesia.tar : 211988480 -> 65008480 (3.261), 98.9 MB/s , 647.0 MB/s
6#silesia.tar : 211988480 -> 62979643 (3.366), 65.2 MB/s , 670.4 MB/s
7#silesia.tar : 211988480 -> 61974560 (3.421), 44.9 MB/s , 688.2 MB/s
8#silesia.tar : 211988480 -> 61028308 (3.474), 32.4 MB/s , 711.9 MB/s
9#silesia.tar : 211988480 -> 60416751 (3.509), 21.1 MB/s , 718.1 MB/s
10#silesia.tar : 211988480 -> 60174239 (3.523), 22.2 MB/s , 721.8 MB/s
> ./compress_zstds/zstd.opt.1 -i10 -b1 -e10 ~/bench/silesia.tar
1#silesia.tar : 211988480 -> 73656930 (2.878), 273.8 MB/s , 722.0 MB/s
2#silesia.tar : 211988480 -> 70162842 (3.021), 203.2 MB/s , 666.6 MB/s
3#silesia.tar : 211988480 -> 66997986 (3.164), 157.4 MB/s , 666.5 MB/s
4#silesia.tar : 211988480 -> 66002591 (3.212), 132.1 MB/s , 661.9 MB/s
5#silesia.tar : 211988480 -> 65008480 (3.261), 96.8 MB/s , 641.6 MB/s
6#silesia.tar : 211988480 -> 62979643 (3.366), 63.1 MB/s , 677.0 MB/s
7#silesia.tar : 211988480 -> 61974560 (3.421), 44.3 MB/s , 678.2 MB/s
8#silesia.tar : 211988480 -> 61028308 (3.474), 33.1 MB/s , 708.9 MB/s
9#silesia.tar : 211988480 -> 60416751 (3.509), 21.5 MB/s , 710.1 MB/s
10#silesia.tar : 211988480 -> 60174239 (3.523), 21.9 MB/s , 723.9 MB/s