[3.x] Fix Line breaking may not work correctly when using color tags with specific font

[Maran23]

Fixes: #108890
Made sure that #34130 is still fixed and does not regress.

The fix is simple:
Since we are running the code in a while loop, we need to assign the spacing_char always and may reset it to 0 when we are in a new blank line (created by ENSURE_WIDTH).

rtl.mp4

cc @lawnjelly

[lawnjelly]

Seems to work okay here.

Although I'm aware this area is prone to regressions, I suspect we'll just have to merge and see how we get on.

[lawnjelly]

Thanks!