fix dialect_name

Co-authored-by: Nicola Soranzo <nicola.soranzo@gmail.com>

sqlalchemy_utils/functions/database.py

@@ -463,8 +463,9 @@ def sqlite_file_exists(database):
     url = copy(make_url(url))
     database, url.database = url.database, None
     engine = None
+    dialect_name = url.get_dialect().name
 
-    if engine.dialect.name.startswith('postgresql'):
+    if dialect_name == 'postgresql':
         ret = False
         for pdb in postgres_db:
             url.database = pdb
@@ -476,13 +477,13 @@ def sqlite_file_exists(database):
                 pass
             engine.dispose()
 
-    elif engine.dialect.name == 'mysql':
+    elif dialect_name == 'mysql':
         engine = sa.create_engine(url)
         text = ("SELECT SCHEMA_NAME FROM INFORMATION_SCHEMA.SCHEMATA "
                 "WHERE SCHEMA_NAME = '%s'" % database)
         ret = bool(get_scalar_result(engine, text))
 
-    elif engine.dialect.name == 'sqlite':
+    elif dialect_name == 'sqlite':
         engine = sa.create_engine(url)
         if database:
             ret = database == ':memory:' or sqlite_file_exists(database)
@@ -501,7 +502,7 @@ def sqlite_file_exists(database):
 
         except (ProgrammingError, OperationalError):
             ret = False
-    
+
     if engine is not None:
         engine.dispose()
     return ret