[flang] Fix crash under -fdebug-dump-all (#66224)

The -fdebug-dump-all flag invokes runtime type information generation
even for a program with fatal semantic errors. This could cause a crash
on a failed CHECK(), since the type information table generator assumes
a correct program. Make it more resilient for a known fatal case. (But
if we hit many more of these, we should look into not generating the
runtime type information tables under this flag.)