Only set indexOffset when the function name is indexed

If a function name contains an equals sign, it doesn't increase the index,
so indexOffset=1 makes Lua see arguments as starting with 0. This change
fixes that, so that indexOffset is only set to 1 if the function name has
an index.

Change-Id: Ifa2dfad4d2f7228c3fd5721ccfc4c235576b663d
Merge "Only set indexOffset when the function name is indexed"