dbusxx-xml2cpp: Only generate argument reader if there are arguments.

This shuts gcc-4.6 up about a variable being written to but not used. See
http://code.google.com/p/chromium-os/issues/detail?id=15109 for an example.

BUG=chromium-os:15109
TEST=Adhoc
Built, built cromo, built gobi-cromo-plugin.

Change-Id: I0ad5185b4f5a91b9ea7c4d5fdcfb10debcbac66b
Signed-off-by: Elly Jones <[email protected]>
Reviewed-on: http://gerrit.chromium.org/gerrit/789
Reviewed-by: Jason Glasgow <[email protected]>
1 file changed