After quite some time debugging going back through previous commits for this
feature and digging around the internals of the blenfont,I finally found the
culprit. It turns out that there was just a single line missing between
BLF_width_default() and BLF_width_and_height_default(), which caused the widths
returned to understimate the space required or so, causing text clipping. The
offending line probably correcting for different DPI scaling values.