Add explicit test for file not found

...caching the metadata moved where ParquetTable did I/O,
which introduced a segfault on not found

tests/test-non-existent

@@ -0,0 +1,33 @@
+#!/bin/bash
+set -euo pipefail
+
+# Verify that loading a non existent file is an error, not a segfault
+
+load_nonexistent() {
+  cat <<EOF
+.echo on
+.load parquet/libparquet
+.testcase notfound
+.bail on
+CREATE VIRTUAL TABLE test USING parquet('$root/doesnotexist.parquet');
+SELECT 123;
+EOF
+}
+
+
+main() {
+  root=$(dirname "${BASH_SOURCE[0]}")/..
+  root=$(readlink -f "$root")
+  cd "$root"
+
+  #This line will exit with non-zero in case of a segfault.
+  "$root"/sqlite/sqlite3 -init <(load_nonexistent) < /dev/null > /dev/null 2> testcase-stderr.txt
+
+  # We expect the 'SELECT 123' command to NOT have been run
+  if grep -q 123 testcase-out.txt; then
+    echo "...FAILED; expected an error message. Check testcase-{out,err}.txt" >&2
+    exit 1
+  fi
+}
+
+main "$@"