[zstd] Fix seqStore growth

We could undersize the literals buffer by up to 11 bytes,
due to a combination of 2 bugs:
* The literals buffer didn't have `WILDCOPY_OVERLENGTH` extra
  space, like it is supposed to.
* We didn't check the literals buffer size in `ZSTD_sufficientBuff()`.

lib/common/zstd_internal.h

@@ -193,6 +193,7 @@ typedef struct {
     BYTE* mlCode;
     BYTE* ofCode;
     size_t maxNbSeq;
+    size_t maxNbLit;
     U32   longLengthID;   /* 0 == no longLength; 1 == Lit.longLength; 2 == Match.longLength; */
     U32   longLengthPos;
 } seqStore_t;