LocalsStorage: fix is user frame slot check

Author: cosminbasca

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/common/LocalsStorage.java

@@ -220,10 +220,13 @@ public Object forEachUntyped(ForEachNode<Object> node, Object arg) {
         bailout();
         Object result = arg;
         for (FrameSlot slot : this.frame.getFrameDescriptor().getSlots()) {
-            if (isUserFrameSlot(slot)) {
-                Object value = getValue(slot);
-                if (value != null) {
-                    result = node.execute(slot.getIdentifier(), result);
+            Object identifier = slot.getIdentifier();
+            if (identifier instanceof String) {
+                if (isUserFrameSlot(identifier)) {
+                    Object value = getValue(slot);
+                    if (value != null) {
+                        result = node.execute(identifier, result);
+                    }
                 }
             }
         }

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/argument/keywords/CopyKeywordsNode.java

@@ -82,7 +82,7 @@ public CopyKeywordsState(HashingStorage hashingStorage, PKeyword[] keywords) {
         }
 
         void addKeyword(String key, Object value) {
-            assert i < keywords.length: "CopyKeywordsNode: current index (over hashingStorage) exceeds keywords array length!";
+            assert i < keywords.length : "CopyKeywordsNode: current index (over hashingStorage) exceeds keywords array length!";
             keywords[i++] = new PKeyword(key, value);
         }