Ignore -fanalyzer-null-argument in pgtkterm.c

Ignore -fanalyzer-null-argument in pgtkterm.c

* src/pgtkterm.c: Ignore -Wanalyzer-null-dereference.
I don’t have time to look into all the diagnostics,
but the ones I checked seemed to be false alarms with
gcc -std=gnu23 on x86-64, and we are ignoring this
diagnostic in other modules.  This is GCC 14.2.1
20250110 (Red Hat 14.2.1-7).

(cherry picked from commit 8d8272d02e38ee3624cd3f16767f3c60fb3383ea)