SetInitialPinDialog: various fixes

• Properly handle Ongoing state: don't enable next step already
• Properly handle cancelling: re-enable step, don't enable next step
• Clear the label of a step when re-starting it.

Fixes kolab/issue4135 (gpg4win) and kolab/issue4134 (gpg4win)

svn path=/branches/kdepim/enterprise4/kdepim/; revision=1091001