Is this the law that catches all the criminals?Some counties (at least here in Suffolk) prohibit you from making any stops whatsoever when travelling from your house to the range if you have a sportsman endorsement. The reason they prohibited stops is because people were doing exactly what you desribed. I would imagine if you live in a county that doesn't prohibit stops and enough people give the "oh I was just on my way to the range" at 2am, when you clearly weren't, that your county will soon prohibit stops as well.
In addition, although carrying outside the scope of your endorsement is not a crime per se, whether or not you will be charged with a crime is a different story. Depending on the circumstances, you could be arrested and charged with a crime akin to menacing in the 2nd degree. It all depends on how visible your firearm is, and what the circumstances were that alerted the athorities to the fact that you were carrying.