Always show WAIT/PAUSE in dialer overflow menu.

Used to hide menu items when not applicable.  Now we show them always
and only perform the action in those cases where menu items were
previously visible.

Updated code to do zero-position checks when there is no
selection...previously missing check.

Changed code to use chars instead of Strings when dealing with single
digits.

Consolidated duplicate code with updateDialString() function.

bug: 7478840
Change-Id: I2aa5d3badd40079e9aa75abf7e4051f9dba5e667