Fix error in concurrent circular eval

Unconditional approximation updates caused unsafe update of attribute value,
didn't match the reference algorithm.

src/template/concurrent/Circular.tt

@@ -84,16 +84,15 @@ $else
 $endif
           state.setChangeInCycle();
           $include(AttrDecl.traceCircularCase1Change)
-        }
 $if(#getNTA)
           if (_next != null) {
             _next.setParent(#ntaParent);
           }
 $endif
-        // Always update the approximation, so that the !canRewrite() NTA case is handled correctly.
           if (!#(signature)_value.compareAndSet(_previous, _next)) {
             _next = (#boxedType) #(signature)_value.get();
           }
+        }
         _previous = _next;
         #tracePrintStartingCycle
         #cycleLimitCheck
@@ -121,8 +120,6 @@ $else
 $endif
         state.setChangeInCycle();
         $include(AttrDecl.traceCircularCase2Change)
-      }
-      // Always update the approximation, so that the !canRewrite() NTA case is handled correctly.
 $if(#getNTA)
         if (_next != null) {
           _next.setParent(#ntaParent);
@@ -131,6 +128,7 @@ $endif
         if (!#(signature)_value.compareAndSet(_previous, _next)) {
           _next = (#boxedType) #(signature)_value.get();
         }
+      }
       $TracePrintReturnNewValue
       $include(AttrDecl.traceCircularExitCase2)
       return _next;
@@ -198,8 +196,6 @@ $else
 $endif
           state.setChangeInCycle();
           $include(AttrDecl.traceCircularCase1Change)
-        }
-        // Always update the approximation, so that the !canRewrite() NTA case is handled correctly.
 $if(#getNTA)
           if (_next != null) {
             if (#(signature)_list.get() == null) {
@@ -213,6 +209,7 @@ $endif
           if (!_value.compareAndSet(_previous, _next)) {
             _previous = (#boxedType) _value.get();
           }
+        }
         #tracePrintStartingCycle
         #cycleLimitCheck
       } while (state.testAndClearChangeInCycle());
@@ -239,8 +236,6 @@ $else
 $endif
         state.setChangeInCycle();
         $include(AttrDecl.traceCircularCase2Change)
-      }
-      // Always update the approximation, so that the !canRewrite() NTA case is handled correctly.
 $if(#getNTA)
         if (_next != null) {
           if (#(signature)_list.get() == null) {
@@ -254,6 +249,7 @@ $endif
         if (!_value.compareAndSet(_previous, _next)) {
           _next = (#boxedType) _value.get();
         }
+      }
       $TracePrintReturnNewValue
       $include(AttrDecl.traceCircularExitCase2)
       return _next;