* encoder_lua: Handle explicitly positive infinity
* encoder_lua: Fix inclusion of pre-/suffix when prettyPrinted
It seems certain operations like --prettyPrint or subset selections does
not produce a DocumentNode, which is where the lua pre- and suffix was
printed, causing those to be omitted.
* encoder_lua: Improve Tag handling robustness
Using the method call seems more reliable in case the input parser
forgets to set the tag.
