Bugfix: Setting dial_retrieve_last was not used in dialpad.

The setting exists in the menu, but regardless if the option was actived
or not, it always retrieved the last called number when pressing the
dialbutton and nothing entered before.
Added a check for this setting. Also removed a duplicate check in
onClick(), which is already done in dialButtonPressed().

An other possibility would be the removing of this setting. Not sure
which is intended.

Change-Id: Ia480105b5f6697c7a422acecea2fceebf16fd71f