Detect optional db struct

I tried nilaway over a piece of code that recentely had a panic.

```go
// definition
type Event struct {
     ...
	Indexes *Indexes `gorm:"embedded;embeddedPrefix:indexes_"`
}
```

In another file

// Indexes was nil 
```go
event.Indexes.Anything
```


nilaway didn't detect this while It seemed quite an obvious panic risk