encoding/json: Fix struct marshal() emitting comma after omitted field

Previously:
```odin
package main

import "core:fmt"
import "core:encoding/json"

T :: struct {
	a: string `json:",omitempty"`,
	b: string,
}

main :: proc() {
	data, _ := json.marshal(T{b = "foo"})
	fmt.println(string(data))
}
```
would output:
```
{,"b":"foo"}
```

which is not correct.

Also cleaned up some whitespace while I'm at it.

0 files changed, 0 insertions, 0 deletions