If followed by '(' (with or without space inbetween) an identifier can
not be a column/row label. Prevent arbitrary content detection in case a
macro function of the same name is meant (fdo#59583) or if it wouldn't
resolve to a known function name at all, that earlier resulted in #REF!
instead of #NAME? in the case of unknown function but label found.

Change-Id: Id36a0c9ebad2d62867b4f9fe00ae78d464e77109