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
"not a statement: result not used from " + operation.name + " operation " + "[" + operation.symbol + "]"
                )
            );
        }
        AExpression userLeftNode = userBooleanCompNode.getLeftNode();
        semanticScope.setCondition(userLeftNode, Read.class);
        semanticScope.putDecoration(userLeftNode, new TargetType(boolean.class));
        checkedVisit(userLeftNode, semanticScope);
        decorateWithCast(userLeftNode, semanticScope);
        AExpression userRightNode = userBooleanCompNode.getRightNode();
        semanticScope.setCondition(userRightNode, Read.class);
        semanticScope.putDecoration(userRightNode, new TargetType(boolean.class));
        checkedVisit(userRightNode, semanticScope);
        decorateWithCast(userRightNode, semanticScope);
        semanticScope.putDecoration(userBooleanCompNode, new ValueType(boolean.class));
    }
    /**
     * Visits a comp expression which covers mathematical comparision operators.
     * Checks: type validation
     */
    @Override
    public void visitComp(EComp userCompNode, SemanticScope semanticScope) {
        Operation operation = userCompNode.getOperation();
        if (semanticScope.getCondition(userCompNode, Write.class)) {
            throw userCompNode.createError(
                new IllegalArgumentException(
                    "invalid assignment: cannot assign a value to " + operation.name + " operation " + "[" + operation.symbol + "]"
                )
            );
        }