Fix unbound cell handler

Author: msimacek

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/bytecode/PBytecodeRootNode.java

@@ -3236,7 +3236,7 @@ private PException bytecodeRaiseVarargs(VirtualFrame virtualFrame, int stackTop,
 
     private void raiseUnboundCell(Node[] localNodes, int bci, int oparg, boolean useCachedNodes) {
         PRaiseNode raiseNode = insertChildNode(localNodes, bci, UNCACHED_RAISE, PRaiseNodeGen.class, NODE_RAISE, useCachedNodes);
-        if (oparg < freeoffset) {
+        if (oparg < cellvars.length) {
             throw raiseNode.raise(PythonBuiltinClassType.UnboundLocalError, ErrorMessages.LOCAL_VAR_REFERENCED_BEFORE_ASSIGMENT, cellvars[oparg]);
         } else {
             int varIdx = oparg - cellvars.length;