diagnostics: fix ICE on fix-it hints on very long lines [PR99323]
PR c/99323 describes an ICE due to a failed assertion deep inside the
fix-it printing machinery, where the fix-it hints on one line have not
been properly sorted in layout's constructor.
The underlying issue occurs when multiple fix-it hints affect a line
wider that LINE_MAP_MAX_COLUMN_NUMBER, where the location_t values for
characters after that threshold fall back to having column zero.
It's not meaningful to try to handle fix-it hints without column
information, so this patch rejects them as they are added to the
rich_location, falling back to the "no fix-it hints on this diagnostic"
case, fixing the crash.