Escape tokenize argument in enable_fts (#828)

The tokenize value passed to Table.enable_fts() was interpolated directly
into the CREATE VIRTUAL TABLE statement inside a single-quoted string
literal. A value containing a single quote could break out of that literal
and inject arbitrary SQL, which executes via executescript(). This is
reachable from the CLI via 'enable-fts --tokenize'.

Route the value through the existing Database.quote() helper so SQLite
itself escapes it. Legitimate tokenizers such as 'porter' are unaffected.
Adds a regression test.

tests/test_fts.py

@@ -252,6 +252,18 @@ def test_fts_tokenize(fresh_db, fts_version):
     }.items() <= rows[0].items()
 
 
+def test_fts_tokenize_escaped(fresh_db):
+    # A malicious tokenize value must not be able to break out of the
+    # string literal in the CREATE VIRTUAL TABLE statement.
+    table = fresh_db["searchable"]
+    table.insert_all(search_records)
+    malicious = "porter'); CREATE TABLE injected(x); --"
+    with pytest.raises(Exception):
+        table.enable_fts(["text"], tokenize=malicious)
+    # The injected statement must not have executed
+    assert "injected" not in fresh_db.table_names()
+
+
 def test_optimize_fts(fresh_db):
     for fts_version in ("4", "5"):
         table_name = f"searchable_{fts_version}"