Only adjust negative indexes in json_get up to the length of the path.
Only adjust negative indexes in json_get up to the length of the path.

The previous code resulted in memory access beyond the path bounds. The
cure is to move it into a code branch that checks the value of lex_level
is within the correct bounds.

Bug reported and diagnosed by Piotr Stefaniak.

zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl,zeroae/postgres-xl