eliminate lingering attribute goals

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "scryer-prolog"
-version = "0.8.111"
+version = "0.8.112"
 authors = ["Mark Thom <markjordanthom@gmail.com>"]
 build = "build.rs"
 repository = "https://github.com/mthom/scryer-prolog"

src/prolog/fixtures.rs

@@ -191,7 +191,7 @@ impl<'a> VariableFixtures<'a> {
 
         for term_ref in iter {
             if let &TermRef::Var(lvl, cell, ref var) = &term_ref {
-                let mut status = self.perm_vars.remove(var).unwrap_or((
+                let mut status = self.perm_vars.swap_remove(var).unwrap_or((
                     VarStatus::Temp(chunk_num, TempVarData::new(lt_arity)),
                     Vec::new(),
                 ));

src/prolog/machine/attributed_variables.rs

@@ -34,6 +34,7 @@ impl AttrVarInitializer {
     pub(super) fn reset(&mut self) {
         self.attr_var_queue.clear();
         self.bindings.clear();
+	self.attribute_goals.clear();
     }
 }