Hopefully fix TOCTOU by calling fopen() before stat()
At least this should prevent Coverity to complain about it:
CID 1090346 (#1 of 1): Time of check time of use (TOCTOU)
fs_check_call: Calling function "stat(char const *, struct stat *)" to perform check on "filename".
toctou: Calling function "fopen(char const * restrict, char const * restrict)" that uses "filename" after a check function. This can cause a time-of-check, time-of-use race condition.
Note that it seems pretty hard to avoid completely:
https://en.wikipedia.org/wiki/Time_of_check_to_time_of_use#Preventing_TOCTTOU
679897d0a1