Fix panic for empty statement block

_test/a9.go

@@ -2,7 +2,10 @@ package main
 
 import "fmt"
 
-var samples = []int{}
+var (
+	samples = []int{}
+	b       = 1
+)
 
 func main() {
 	samples = append(samples, 1)

_test/fun4.go

@@ -0,0 +1,11 @@
+package main
+
+func f() {}
+
+func main() {
+	f()
+	println("ok")
+}
+
+// Output:
+// ok

_test/provider/foo.go

@@ -9,3 +9,8 @@ func Foo() {
 func F1() {
 	fmt.Println("SomeString:", SomeString)
 }
+
+//func F2() {
+//var buf [SomeInt]byte
+//fmt.Println("buf:", buf)
+//}

interp/cfg.go

@@ -331,7 +331,9 @@ func (interp *Interpreter) Cfg(root *Node) []*Node {
 
 		case BlockStmt:
 			wireChild(n)
-			n.findex = n.child[len(n.child)-1].findex
+			if len(n.child) > 0 {
+				n.findex = n.child[len(n.child)-1].findex
+			}
 			scope = scope.pop()
 
 		case ConstDecl:
@@ -450,7 +452,7 @@ func (interp *Interpreter) Cfg(root *Node) []*Node {
 							n.fsize = 0
 						}
 					} else {
-						log.Println(n.index, "resolve method")
+						log.Println(n.index, "unresolve call")
 						// method must be resolved here due to declaration after use
 					}
 					n.child[0].findex = -1 // To force reading value from node instead of frame (methods)

interp/interp_test.go

@@ -292,7 +292,10 @@ package main
 
 import "fmt"
 
-var samples = []int{}
+var (
+	samples = []int{}
+	b       = 1
+)
 
 func main() {
 	samples = append(samples, 1)
@@ -916,6 +919,24 @@ func main() {
 	// 18
 }
 
+func Example_fun4() {
+	src := `
+package main
+
+func f() {}
+
+func main() {
+	f()
+	println("ok")
+}
+`
+	i := NewInterpreter(Opt{Entry: "main"})
+	i.Eval(src)
+
+	// Output:
+	// ok
+}
+
 func Example_goroutine() {
 	src := `
 package main