Enhance sqlite3_randomness(N,P) such that it resets the internal PRNG

if N is less than 1.  Subsequent calls to sqlite3_randomness() will reinitialize
the internal PRNG by calling the xRandomness() method of the default VFS.

FossilOrigin-Name: a221aa82bb5496885fd0bf76e4601443799511de

src/random.c

@@ -52,6 +52,12 @@ void sqlite3_randomness(int N, void *pBuf){
   sqlite3_mutex_enter(mutex);
 #endif
 
+  if( N<=0 ){
+    wsdPrng.isInit = 0;
+    sqlite3_mutex_leave(mutex);
+    return;
+  }
+
   /* Initialize the state of the random number generator once,
   ** the first time this routine is called.  The seed value does
   ** not need to contain a lot of randomness since we are not
@@ -79,7 +85,8 @@ void sqlite3_randomness(int N, void *pBuf){
     wsdPrng.isInit = 1;
   }
 
-  while( N-- ){
+  assert( N>0 );
+  do{
     wsdPrng.i++;
     t = wsdPrng.s[wsdPrng.i];
     wsdPrng.j += t;
@@ -87,7 +94,7 @@ void sqlite3_randomness(int N, void *pBuf){
     wsdPrng.s[wsdPrng.j] = t;
     t += wsdPrng.s[wsdPrng.i];
     *(zBuf++) = wsdPrng.s[t];
-  }
+  }while( --N );
   sqlite3_mutex_leave(mutex);
 }
 
@@ -116,7 +123,4 @@ void sqlite3PrngRestoreState(void){
     sizeof(sqlite3Prng)
   );
 }
-void sqlite3PrngResetState(void){
-  GLOBAL(struct sqlite3PrngType, sqlite3Prng).isInit = 0;
-}
 #endif /* SQLITE_OMIT_BUILTIN_TEST */