Check if dict is empty before reading first byte

lib/legacy/zstd_v05.c

@@ -1873,10 +1873,12 @@ static size_t HUFv05_readStats(BYTE* huffWeight, size_t hwSize, U32* rankStats,
     U32 weightTotal;
     U32 tableLog;
     const BYTE* ip = (const BYTE*) src;
-    size_t iSize = ip[0];
+    size_t iSize;
     size_t oSize;
     U32 n;
 
+    if (!srcSize) return ERROR(srcSize_wrong);
+    iSize = ip[0];
     //memset(huffWeight, 0, hwSize);   /* is not necessary, even though some analyzer complain ... */
 
     if (iSize >= 128)  { /* special header */