BUG/MEDIUM: pattern: a typo breaks automatic acl/map numbering

BUG/MEDIUM: pattern: a typo breaks automatic acl/map numbering

Dmitry Sivachenko reported that nice warning :
src/pattern.c:2243:43: warning: if statement has empty body [-Wempty-body]
                                if (&ref2->list == &pattern_reference);
                                                                      ^
src/pattern.c:2243:43: note: put the semicolon on a separate line to silence
      this warning

It was merged as is with the code from commit af5a29d ("MINOR: pattern:
Each pattern is identified by unique id").

So it looks like we can reassign an ID which is still in use because of
this.