Annex formatter sometimes throws IllegalStateException #2036

To reproduce:

1. Format an AADL file that has an EMV2 annex
2. After that format an AADL file that has some annex X without a plugin for parsing X installed

There is a hack to store parse results. The last parse result from an Xtext parser is kept around even if we are processing an annex that is not xtext related. The last parse result must be cleared in these cases.