[MC-123331] 'execute if/unless score' sets the score to 0 if unset

Using /execute if/unless score and testing for players which do not have a score sets 0 for them and the test succeeds.

Expected would be that the comparison failed and no score was set.

Create a new objective called something like test
Run the following to set the value to test with
```
/scoreboard players set value test 0
```
Run
```
/execute if score something test = value test run say test
```
The command runs successfully even though the player "something" hasn't been initialized in the objective "test"