empty-block: Fix false positive on select {} (#805)

This fixes a false positive reported by revive on the following:

    select {}

This is a way to block the program indefinitely.
It is used in cases like:

- Running a long-running server in a background thread
  and blocking `main` from exiting until the application dies.
  This is something you might do if your process has
  multiple servers/listeners in the same process.

  ```go
  go grpcListenAndServe()
  go httpListenAndServe()
  go logFlusher()

  select {}
  ```

- In programs compiled to WASM to prevent the application from exiting,
  so that the Javascript components may interact with it.

  ```go
  func main() {
    js.Global().Set("foo", foo)
    select {}
  }
  ```

  Without this, one may see an error like,
  "Error: Go program has already exited"

As a workaround, these programs can block forever
by receiving from a throwaway channel (`<-make(chan struct{})`),
but `select {}` is still a completely valid way of doing this,
so supporting it makes sense.

The issue was previously reported in #698 but was closed
because the author was satisfied with a `//nolint` comment.

Now that this rule is part of the default rule set (#799)
the case for addressing the false positive is stronger.

Resolves #804

rule/empty-block.go

@@ -40,6 +40,9 @@ func (w lintEmptyBlock) Visit(node ast.Node) ast.Visitor {
 	case *ast.FuncLit:
 		w.ignore[n.Body] = true
 		return w
+	case *ast.SelectStmt:
+		w.ignore[n.Body] = true
+		return w
 	case *ast.RangeStmt:
 		if len(n.Body.List) == 0 {
 			w.onFailure(lint.Failure{