fix check macro expansion
If the only argument to `check!` is the module name I get this error:
```
error: expected expression, found `,`
--> src/tools/tidy/src/main.rs:63:42
|
57 | / macro_rules! check {
58 | | ($p:ident $(, $args:expr)* ) => {
59 | | drain_handles(&mut handles);
60 | |
... |
63 | | $p::check($($args),* , &mut flag);
| | ^ expected expression
... |
69 | | }
70 | | }
| |_________- in this expansion of `check!`
...
117 | check!(hey);
| ----------- in this macro invocation
```
This change makes it so commas are added only when there are `args`.
r? ```@albertlarsan68```