Only load extra table positions for CDicts

Zstdmt uses prefixes to load the overlap between segments. Loading extra
positions makes compression non-deterministic, depending on the previous
job the context was used for. Since loading extra position takes extra
time as well, only do it when creating a `ZSTD_CDict`.

Fixes #1077.

lib/compress/zstd_fast.c

@@ -14,7 +14,7 @@
 
 void ZSTD_fillHashTable(ZSTD_matchState_t* ms,
                         ZSTD_compressionParameters const* cParams,
-                        void const* end)
+                        void const* end, ZSTD_dictTableLoadMethod_e dtlm)
 {
     U32* const hashTable = ms->hashTable;
     U32  const hBits = cParams->hashLog;
@@ -34,6 +34,9 @@ void ZSTD_fillHashTable(ZSTD_matchState_t* ms,
             size_t const hash = ZSTD_hashPtr(ip + i, hBits, mls);
             if (i == 0 || hashTable[hash] == 0)
                 hashTable[hash] = current + i;
+            /* Only load extra positions for ZSTD_dtlm_full */
+            if (dtlm == ZSTD_dtlm_fast)
+                break;
         }
     }
 }