''A chair of perfect proportions.'' This is how Peter Maly, one of the greatest German designers of his time, defines his product. ''A little like the tuner designed by Dieter Rams for Braun.'' The chair is so perfect one has the impression that it has always existed. It is a score of perfectly harmonious chords, which chimes perfectly with a very broad register of furniture, tables and sideboards. Its proportions are irreproachable, as is the quality of its finish.