Distance field fonts leak memory

Animating a text string (like speed) from application seems to cause memory leak and a drop in performance when running long enough.

It does not matter if the text string is changed with string type DataInput, Float type datainput, or using setAttribute, so the cause does not seem to be in setAttribute/DataInput path.

Happens quite quickly with i.MX8 with B2Qt, at least (used memory doubles in an hour, and FPS drops to one third of the initial).