Prevent flush from creating cursor without con

MysqlRed.flush() tried to create a cursor in any case. If there was no
connection (because the subclasses haven't been instantiated an oursql
Error occured.
Instead, check before if there is a connection and otherwise raise an Error

Related Task: [https://fs.golderweb.de/index.php?do=details&task_id=75 FS#75]

Related Task: [https://fs.golderweb.de/index.php?do=details&task_id=75 FS#75]

mysqlred.py

@@ -92,6 +92,9 @@ class MysqlRed:
         """
         Run cached querys
         """
+        if not cls.connection:
+            raise MysqlRedConnectionError( "No connection exists!" )
+
         cursor = cls.connection.cursor()
 
         # Execute insert query
@@ -307,3 +310,17 @@ article7 ) VALUES ( ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ? );'
                 break
             for row in res:
                 yield row
+
+
+class MysqlRedError(Exception):
+    """
+    Basic Exception class for this module
+    """
+    pass
+
+
+class MysqlRedConnectionError(MysqlRedError):
+    """
+    Raised if there are Errors with Mysql-Connections
+    """
+    pass