Honestly this particular one sounds so funny and interesting, i have never heard of such before in my life that whistling while gambling can cause bad luck, for me I think this act can make one to lose concentration,  that's is what I think though because I don't think superstition works in gambling.  

People may have superstitious when it comes to gambling but I don't think they should be too rely and confident in the believe they have because I know as far as gambling is concerned it can never be predicted.  Gambling is a game of luck and this happens so naturally,  I don't think any believe can influence the luck that is in gambling to take place, if people are too superstitious in gambling I think they may go extreme to gamble so much believing their belief can give them what they want in gambling.