backuppc: Fix TB when listing files

This issue was seen on a Debian Squeeze system:

Sometimes, url can be formatted like this:

&sharename=%2Fcygdrive%2Fc%2FDocuments%26Acirc%3B%2520and%26Acirc%3B%2520Settings%2F

And this "%26Acirc%3B%25" gives a bad array with some keys who
starts with Acirc;_.
These bad keys are part of previous good key value, so this function
try to fix it.

Bad $_GET example:
Array
  (
      [module] => backuppc
      [submod] => backuppc
      [action] => ajaxBrowseFiles
      [filter] =>
      [host] => UUID3
      [sharename] => /cygdrive/c/Documents
      [Acirc;_and] =>
      [Acirc;_Settings/] =>
      [backupnum] => 0
      [location] =>
      [maxperpage] => 20
      [folder] => /
  )