Layout problems with messaging page when no left side blocks

When there are no blocks on the left of the messaging page, the messaging screen layout is messed up.

There are multiple ways to reproduce this, easiest is docking blocks:

Steps to reproduce:

1. Use theme 'more' with a background colour set
2. Login as admin
3. Go to My Profile > Messages
4. Dock any blocks on page

Expected result:

• The 'main' content area surrounds the content

Actual result:

• The main content area background doesn't cover the background.

Another way to reproduce is move the blocks to the right.

Steps to reproduce:

1. Use theme 'more' with a background colour set
2. Login as admin
3. On frontpage turn editing on
4. Go to My Profile > Messages
5. Move all blocks on left to right
6. Go to front page and turn editing off
7. Go to My Profile > Messages