iossim: Fix compilation against SDKs earlier than 10.9

Looks like firstObject is not exported in SDKs ealier than 10.9,
even though the documentation claims differently. Latest Xcode
on OS X 10.7 doesn't provide the 10.9 SDK, so avoid using
firstObject and lastObject

Change-Id: Ia266c6aa2030d4799a3cec13e97ab7175adf5138
Reviewed-by: Kevin Funk <kevin.funk@kdab.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@theqtcompany.com>