Fixes memory error in cases where the length of the language name
returned by uloc_getLanguage() is exactly ULOC_LANG_CAPACITY, in which
case the status is set to U_STRING_NOT_TERMINATED_WARNING.
Also check in call sites for other ICU functions that are expected to
return a C string to be safe (no bug is known at these other call
sites).
Reported-by: Alexander Lakhin
Discussion: https://postgr.es/m/2098874d-c111-41e4-9063-30bcf135226b@gmail.com
1c634f6647