don't compare signed/unsigned

lib/http_ntlm.c

@@ -212,7 +212,7 @@ static void mkhash(char *password,
   static const unsigned char magic[] = {
     0x4B, 0x47, 0x53, 0x21, 0x40, 0x23, 0x24, 0x25
   };
-  int i;
+  unsigned int i;
   size_t len = strlen(password);
 
   /* make it fit at least 14 bytes */