Fix VACUUM with an open transaction

Database.vacuum() passed VACUUM directly to SQLite, which rejects it while a transaction is open. Commit first so the maintenance operation can run, and cover the reported transaction path with a regression test.

Fixes #479

sqlite_utils/db.py

@@ -1897,6 +1897,7 @@ class Database:
 
     def vacuum(self) -> None:
         "Run a SQLite ``VACUUM`` against the database."
+        self.commit()
         self.execute("VACUUM;")
 
     def analyze(self, name: Optional[str] = None) -> None:

tests/test_create.py

@@ -1170,6 +1170,17 @@ def test_vacuum(fresh_db):
     fresh_db.vacuum()
 
 
+def test_vacuum_commits_open_transaction(fresh_db):
+    fresh_db["data"].insert({"foo": "foo"})
+    fresh_db.begin()
+    fresh_db.execute("insert into data (foo) values ('bar')")
+
+    fresh_db.vacuum()
+
+    assert not fresh_db.conn.in_transaction
+    assert [row["foo"] for row in fresh_db["data"].rows] == ["foo", "bar"]
+
+
 def test_works_with_pathlib_path(tmpdir):
     path = pathlib.Path(tmpdir / "test.db")
     db = Database(path)