If a hex literal has an 'd' of 'f' in it, such as '0xf' or '0xd', the compiler fails with illegal tree structure.

The other hex literals work.  The issue is probably related to using `f` and `d` in float and double literals.

```
    public void testHexCollisionDouble() {
        assertEquals(13, exec("return 0xd"));
    }

    public void testHexCollisionFloat() {
        assertEquals(15, exec("return 0xf"));
    }

    public void testHex() throws Exception {
        for (int i = 0; i <= 15; i++) {
            String hex = Integer.toHexString(i);
            if ("d".equals(hex) || "f".equals(hex)) {
                continue;
            }
            assertEquals(i, exec("return 0x" + hex));
            assertEquals(i, exec("return 0x" + hex.toUpperCase(Locale.ROOT)));
            assertEquals(i, exec("return 0X" + hex));
            assertEquals(i, exec("return 0X" + hex.toUpperCase(Locale.ROOT)));
        }
    }
```
modules/lang-painless/src/main/java/org/elasticsearch/painless/phase/DefaultSemanticAnalysisPhase.java
* Checks: control flow, type validation
     */
    @Override
    public void visitExpression(SExpression userExpressionNode, SemanticScope semanticScope) {
        Class<?> rtnType = semanticScope.getReturnType();
        boolean isVoid = rtnType == void.class;
        boolean lastSource = semanticScope.getCondition(userExpressionNode, LastSource.class);
        AExpression userStatementNode = userExpressionNode.getStatementNode();
        if (lastSource && isVoid == false) {
            semanticScope.setCondition(userStatementNode, Read.class);
        }
        checkedVisit(userStatementNode, semanticScope);
        Class<?> expressionValueType = semanticScope.getDecoration(userStatementNode, ValueType.class).valueType();
        boolean rtn = lastSource && isVoid == false && expressionValueType != void.class;
        if (rtn) {
            semanticScope.putDecoration(userStatementNode, new TargetType(rtnType));
            semanticScope.setCondition(userStatementNode, Internal.class);
            decorateWithCast(userStatementNode, semanticScope);
            semanticScope.setCondition(userExpressionNode, MethodEscape.class);
            semanticScope.setCondition(userExpressionNode, LoopEscape.class);
            semanticScope.setCondition(userExpressionNode, AllEscape.class);
        }
    }
    /**
     * Visits a try statement.
     * Checks: control flow
     */
    @Override
    public void visitTry(STry userTryNode, SemanticScope semanticScope) {
        SBlock userBlockNode = userTryNode.getBlockNode();