Raw filters don't seem to be working as intended

Let's say I have a task folder in `~/_sample_data`.
The output of `unset TASKRC; task rc.data.location=~/_sample_data` is (removing the "configuration override" notes):
```
ID Age Tag Description Urg
2 5min habit another task 0.8
1 5min sample task 0

2 tasks
```

I then tried to use it this way:
```python
from tasklib import TaskWarrior
import os

del os.environ["TASKRC"] # just to be sure it isn't my config's fault
tw = TaskWarrior(f"{os.environ['HOME']}/_sample_data")

print(tw.tasks.filter("status:pending")) # yields the two tasks
print(tw.tasks.filter("status:pending +habit")) # yields no task (was supposed to yield one)
print(tw.tasks.filter("+habit")) # yields one task, as expected
print(tw.tasks.filter(status="pending", tag="habit")) # yields one task ~ this one works fine as well
```

The shown output is then:
```
[sample task, another task]
[]
[another task]
[another task]
```
But what was expected:
```
[sample task, another task]
[another task]
[another task]
[another task]
```
It seems like only raw filters that have more than one condition are affected by this.