Revert "Fixed bug in debug_assert"

This reverts commit 7e95206c.

src/context.rs

@@ -100,14 +100,18 @@ impl<'d, 'f: 'd> MutContext<'d, 'f> {
             "_apply_overlay: Interpreter bug, overlay is leaking a strategy definition"
         );
         for (name, value) in scope.term {
-            let value = value.expect(
-                "_apply_overlay: Interpreter bug, unintialised variable in overlay"
-            );
-            let result = self.match_term(&name, &value);
-            debug_assert!(
-                result.is_ok(),
-                "_apply_overlay: Interpreter bug, overlay has names that were bound underneath"
-            );
+            if let Some(value) = value {
+                let result = self.match_term(&name, &value);
+                debug_assert!(
+                    result.is_ok(),
+                    "_apply_overlay: Interpreter bug, overlay has names that were bound underneath"
+                );
+            } else {
+                unreachable!(
+                    "_apply_overlay: Interpreter bug, who put an uninitialised variable in \
+                              my overlay? >:("
+                )
+            }
         }
 
     }
@@ -117,11 +121,7 @@ impl<'d, 'f: 'd> MutContext<'d, 'f> {
             "apply_overlay: Interpreter bug, unexpected end of stack",
         );
         debug_assert!(
-            match scope.kind {
-                ScopeKind::Normal => false,
-                ScopeKind::Overlay => true,
-                ScopeKind::InvalidatedOverlay(_) => true,
-            },
+            scope.kind == ScopeKind::Overlay,
             "apply_overlay: Interpreter bug, unexpected non-overlay scope"
         );
         self._apply_overlay(scope);