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
throw userBlockNode.createError(new IllegalArgumentException("invalid block: unreachable statement"));
                }
            }
            anyContinue |= semanticScope.getCondition(userStatementNode, AnyContinue.class);
            anyBreak |= semanticScope.getCondition(userStatementNode, AnyBreak.class);
        }
        if (anyContinue) {
            semanticScope.setCondition(userBlockNode, AnyContinue.class);
        }
        if (anyBreak) {
            semanticScope.setCondition(userBlockNode, AnyBreak.class);
        }
    }
    /**
     * Visits an if statement with error checking for an extraneous if.
     * Checks: control flow
     */
    @Override
    public void visitIf(SIf userIfNode, SemanticScope semanticScope) {
        AExpression userConditionNode = userIfNode.getConditionNode();
        semanticScope.setCondition(userConditionNode, Read.class);
        semanticScope.putDecoration(userConditionNode, new TargetType(boolean.class));
        checkedVisit(userConditionNode, semanticScope);
        decorateWithCast(userConditionNode, semanticScope);
        SBlock userIfBlockNode = userIfNode.getIfBlockNode();
        if (userConditionNode instanceof EBooleanConstant || userIfBlockNode == null) {
            throw userIfNode.createError(new IllegalArgumentException("extraneous if block"));
        }
        semanticScope.replicateCondition(userIfNode, userIfBlockNode, LastSource.class);
        semanticScope.replicateCondition(userIfNode, userIfBlockNode, InLoop.class);