Postgres backend - key property inferences crashes with segfault

[lordpretzel]

to reproduce the bug

sudo docker run -d --name mypostgres --rm -p 5432:5432 iitdbgroup/cs425
./src/command_line/gprom -backend postgres -host 127.0.0.1 -port 5432 -user postgres -passwd test -db cs425 -heuristic_opt -loglevel 0
GProM Commandline Client
Please input a SQL command, '\q' to exit the program, or '\h' for help
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Oracle SQL - Postgres:postgres@127.0.0.1:cs425$SELECT * FROM "student";
Segmentation fault: 11