multi-select element in unban email-adresses not limited in width

In MCP in the mcp_ban module where you can ban/unban email-adresses the multi-select element with all the banned email-addresses is not limited in it's width so it overlaps with the borders of the page if an email-address is long enough.

Steps to reproduce:
1. Ban a very very long email-address
2. Adjust the width of your window and see what happens.