fix #12051: close img tag

Fixes http://trac.openmicroscopy.org.uk/ome/ticket/12051.
Open the webclient login page, make sure the padlock looks okay
![nuvola_encrypted_grey16](https://f.cloud.github.com/assets/2630707/2459614/9535676c-af5e-11e3-9e06-84823834d5af.png)
and look at the source.
Cc: @manics