rearange ArrayIndexingStep to avoid #shared predicate

Author: erik-krogh

javascript/ql/src/semmle/javascript/Arrays.qll

@@ -156,9 +156,8 @@ private module ArrayDataFlow {
 
     ArrayIndexingStep() {
       read = this and
-      forex(InferredType type | type = read.getPropertyNameExpr().flow().analyze().getAType() |
-        type = TTNumber()
-      ) and
+      TTNumber() =
+        unique(InferredType type | type = read.getPropertyNameExpr().flow().analyze().getAType()) and
       exists(VarAccess i, ExprOrVarDecl init |
         i = read.getPropertyNameExpr() and init = any(ForStmt f).getInit()
       |