Fixes Xcode workspace generation failure

Fixes this error:

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-- ...bin/scripts/ide/xcode.lua:182: attempt to index field '?' (a nil value):
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stack traceback:
	...usNextGen/bin/macosx32/../scripts/JamToWorkspace.lua:121: in function <...usNextGen/bin/macosx32/../scripts/JamToWorkspace.lua:97>
	.../bin/scripts/ide/xcode.lua:182: in function 'XcodeHelper_GetProjectExportInfo'
	.../bin/scripts/ide/xcode.lua:582: in function 'Write'
	.../bin/macosx32/../scripts/JamToWorkspace.lua:554: in function 'DumpProject'
	.../bin/macosx32/../scripts/JamToWorkspace.lua:664: in function 'DumpWorkspace'
	.../bin/macosx32/../scripts/JamToWorkspace.lua:988: in function <.../bin/macosx32/../scripts/JamToWorkspace.lua:702>
	[C]: in function 'xpcall'
	.../bin/macosx32/../scripts/JamToWorkspace.lua:1066: in main chunk
	[C]: ?
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