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{

testdata/empty-block.go

@@ -2,6 +2,8 @@
 
 package fixtures
 
+import "net/http"
+
 func f(x int) {} // Must not match
 
 type foo struct{}
@@ -9,6 +11,12 @@ type foo struct{}
 func (f foo) f(x *int)  {} // Must not match
 func (f *foo) g(y *int) {} // Must not match
 
+
+func h() {
+	go http.ListenAndServe()
+	select {} // Must not match
+}
+
 func g(f func() bool) {
 	{ // MATCH /this block is empty, you can remove it/
 	}
@@ -44,4 +52,9 @@ func g(f func() bool) {
 	for range s { // MATCH /this block is empty, you can remove it/
 	}
 
+	select {
+	case _, ok := <-c:
+		if ok { // MATCH /this block is empty, you can remove it/
+		}
+	}
 }