only exit if silent install or portable copy starting (#12455)

#12431 introduced a change where NVDA always exits at the end of creating a portable copy. The intention was to change the behaviour 

from
exit NVDA if it is a silent install
to
exit NVDA if it is a silent install, or if we are starting the portable copy.

As a result of #12431, finishing the install of a portable copy without starting it also results in NVDA exiting.

source/gui/installerGui.py

@@ -482,4 +482,5 @@ def doCreatePortable(portableDirectory,copyUserConfig=False,silent=False,startAf
 			def startNewPortableNVDAInstance():
 				_startNewNVDAInstance(portableDirectory)
 			core.preNVDAExit.register(startNewPortableNVDAInstance)
-	core.triggerNVDAExit()
+	if silent or startAfterCreate:
+		core.triggerNVDAExit()