Issue title: Truncate statement not recognized
 Issue body: Statement does not exist in ABAPv755(or parser error).
Statement exist even in 755.

data:
  i_filename type c length 255 value '/user/sap/data/....'.

truncate dataset i_filename at current position.
 Comments: 
 Comment 0: ```abap
data i_filename type c length 255 value '/user/sap/data/....'.
truncate dataset i_filename at current position.
```
 Comment 1: heh, there are always more ABAP statements :)
{'source': 'GithubIssues', 'repo_name_with_owner': 'abaplint/abaplint', 'issue_id': 812568935, 'repo_stars': 127.0}