Fix nxu:set tag when caching and resolving the expression twice

When setting both attributes cache and resolveTwice to true, the final result should be put in cache.
Currently only the first resolution is put in cache, so any subsequent resolutions will be done later, which is not the intended behavior of the "cache" attribute.

This is a problem for components that do not perform EL expression resolution correctly, or need to handle functions in the second resolution like CSV Seam JSF library that handle export of content views, dealing with functions like nxu:basicDateFormatter(): the function mapper may not be available to resolve these functions on the second resolution.