Allow zero length inputs to _wc_Hash_Grow to be a succesful no-op

Author: night1rider

wolfcrypt/src/hash.c

@@ -1956,9 +1956,12 @@ int _wc_Hash_Grow(byte** msg, word32* used, word32* len, const byte* in,
 {
     word32 usedSz = 0;
 
-    if (inSz <= 0 || !WC_SAFE_SUM_WORD32(*used, (word32)inSz, usedSz))
+    if (inSz < 0 || !WC_SAFE_SUM_WORD32(*used, (word32)inSz, usedSz))
         return BAD_FUNC_ARG;
 
+    if (inSz == 0)
+        return 0;
+
     if (*len < usedSz) {
         if (*msg == NULL) {
             *msg = (byte*)XMALLOC(usedSz, heap, DYNAMIC_TYPE_TMP_BUFFER);