Update 0002-enable-md-pg_duckdb.sql (#932)

Update 0002-enable-md-pg_duckdb.sql to make it compatible with
Postgresql 14.

Resolves #928

Author: hannosgit

docker/init.d/0002-enable-md-pg_duckdb.sql

@@ -1,12 +1,19 @@
 -- This script is used to enable MotherDuck support if
 -- the token is provided in the environment variables.
 
-\getenv lc_token motherduck_token
-\getenv uc_token MOTHERDUCK_TOKEN
+-- Once we stop supporting PG14 we can use \getenv again
+-- For grepability: PG_VERSION_NUM < 150000
+\set lc_token `echo $motherduck_token`
+\set uc_token `echo $MOTHERDUCK_TOKEN`
 
-\if :{?lc_token}
+SELECT
+    LENGTH(:'lc_token') > 0 as lc_token_set,
+    LENGTH(:'uc_token') > 0 as uc_token_set
+\gset
+
+\if :lc_token_set
     CALL duckdb.enable_motherduck(:'lc_token'::TEXT);
-\elif :{?uc_token}
+\elif :uc_token_set
     CALL duckdb.enable_motherduck(:'uc_token'::TEXT);
 \else
     -- MotherDuck was not enabled, so we can skip the rest of the script