Fix for QAT RNG to allow zero length. Resolves PSS test case where wc_RNG_GenerateBlock is called for saltLen == 0.

Author: dgarske

wolfcrypt/src/port/intel/quickassist.c

@@ -3343,10 +3343,15 @@ int IntelQaDrbg(WC_ASYNC_DEV* dev, byte* rngBuf, word32 rngSz)
     CpaFlatBuffer* pOut = NULL;
     word32 idx = 0, gen = 0;
 
-    if (dev == NULL || rngBuf == NULL || rngSz == 0) {
+    if (dev == NULL || rngBuf == NULL) {
         return BAD_FUNC_ARG;
     }
 
+    /* This function can be called with rngSz == 0 */
+    if (rngSz == 0) {
+        return 0; /* no data to get */
+    }
+
 #ifdef QAT_DEBUG
     printf("IntelQaDrbg: dev %p, buf %p, sz %d\n", dev, rngBuf, rngSz);
 #endif