Usage message is displayed when not desired.

When I build a class with methods that can be chained (they return `self`), I find that the "commands" help message is written out even when I provide commands with proper arguments and the commands are executed. Here is the code
```
from __future__ import annotations
from fire import Fire

class Foo:
def act(self, x: int) -> Foo:
"""
Act for some number of minutes.
Parameters
----------
x : int
The number of minutes to act.
"""

print("act", x, "minute(s)")
return self

def rest(self, x: int, y: str = "hours") -> Foo:
"""
Rest for a while.
Parameters
----------
x : int
The time to rest.
y : str
The units of x. The default is hours.
"""

print("rest", x, y)
return self

if __name__ == "__main__":
Fire(Foo)
```

If I run this as `python fire_bug.py`, I get the help output I expect, which is
```
NAME
fire_bug.py act 1

SYNOPSIS
fire_bug.py act 1 COMMAND

COMMANDS
COMMAND is one of the following:

act
Act for some number of minutes.

rest
Rest for a while.
```
If I run this as `python fire_bug.py act 1`, I unexpectedly get the help output
```
NAME
fire_bug.py act 1

SYNOPSIS
fire_bug.py act 1 COMMAND

COMMANDS
COMMAND is one of the following:

act
Act for some number of minutes.

rest
Rest for a while.
```
followed by the output I expect, which is
```
act 1 minute(s)
```

If run this as `python fire_bug.py act 1 rest 9`, I again unexpectedly get the help output
```
NAME
fire_bug.py act 1 rest 9

SYNOPSIS
fire_bug.py act 1 rest 9 - COMMAND

COMMANDS
COMMAND is one of the following:

act
Act for some number of minutes.

rest
Rest for a while.
```
followed by the output I expect, which is
```
act 1 minute(s)
rest 9 hours
```
If I add a `__str__` method to the class that returns `"\b"`, I don't get the unexpected messages, but I also don't get a help message if I run `python fire_bug.py`.

As a general observation, running `python fire_bug.py --help` does not produce useful output. The output is
```
NAME
fire_bug.py

SYNOPSIS
fire_bug.py -
```
The output I would expect would be the output I get when I run `python fire_bug.py`. I am aware that if I have an `__init__` method with arguments that the information about those arguments will be displayed, but separating the two sets of information in this way is quite counterintuitive. Both sets of information should be provided when running with no command and when running with only a `--help` argument.