Maximum distance of lines in screen space is limited. This limit seems
reasonable for FPS higher than 1, but UI allows to set 0.01 FPS with
soft. even lower values are possible.

This patch allows for normal operation within soft limits and labels are
still visible and quite usable within hard limits.

At about 1/4000 FPS label values starts to overflow, but this is not
effect of this patch and overflow can be caused.