See issue i34904 for motivation.

Scenario:
1. Java script calls XClosable::close() at an Impress document.
2. Eventually DrawViewShell::PrepareClose() is called from the SfxBaseController
to ask whether it may be closed or not. In the negative case two tasks are executed:
a. PrepareClose() starts the aCloseTimer which eventually calls CloseHdl which
in turn dispatches the SID_CLOSEWIN slot. 
b. PrepareClose() returns 0 which makes the SfxBaseController throw a
CoseVetoException.

Problem:
The asynchronous call of the SID_CLOSEWIN slot leads eventually to the display
of a message box that tells the (nonexistent) user that the document was
modified.  This box blocks the script.

Solution:
According to MBA the two actions a) and b) have to be done by the
SfxBaseController:  the one who throws the exception is responsible for closing
the document.  
To avoid the message box PrepareClose() must not start the aCloseTimer (except
when it is called with TRUE, i.e. not as result of an API call.)

This issue is about not starting the aCloseTimer.