TextLayout: Clarify implementation of special case

TextLayout: Clarify implementation of special case

This exists to exit early for invisible lines. It attempts to use the
LineDisplay’s direction to create a corresponding PangoLayout. However,
the dir is not yet set by this point, & the display was new0()d, so its
dir is always 0 == TEXT_DIR_NONE. Thus, we always create an LTR layout.

Whatever the original intent, this outcome seems to be OK, so let’s make
the code say what it means, rather than using a misleading conditional.

https://bugzilla.gnome.org/show_bug.cgi?id=779099