'Gomango' is onto something. I think he is suggesting to fill the paint crack with a filler and repaint it or strip the area back and fill it with bronze or silver solder. Lots of frames have gaps between the tube and the lug and as 'repechage' says, "The painter is the brazers best friend, or can be." Painters can hide poor brazing jobs by applying a thick coat of paint. As he also says, you cannot allow water, etc, to get into the gap and cause real problems. Fortunately, your frame looks to be just painted as well as being very clean and most probably free of corrosion.

As you indicate. the area is not cracked and you can see the bronze. It's probably just a poor brazing job on that area of the joint. 'Repechage' is not worried that the joint braking and neither would I be.

My suggestion, as I said before is to touch up the paint to fill the gap and match the colour (perhaps that's a little more than I said before).