don't count the terminator in PStrIter len

src/prolog/examples/plres.pl

@@ -31,6 +31,7 @@
 
 :- use_module(library(dcgs)).
 :- use_module(library(dif)).
+:- use_module(library(format)).
 :- use_module(library(lists)).
 
 pl_resolution(Clauses0, Chain) :-

src/prolog/machine/partial_string.rs

@@ -200,7 +200,7 @@ impl PartialString {
 
     #[inline]
     pub fn range_from(&self, index: RangeFrom<usize>) -> PStrIter {
-        PStrIter::from(self.buf, self.len, index.start)
+        PStrIter::from(self.buf, self.len - '\u{0}'.len_utf8(), index.start)
     }
 
     #[inline]