fix the bug reflect on zero Value

fix the bug ：reflect: call of reflect.Value.Type on zero Value

if the slice is nil， or len==0， will be panic.
the case:

type Foo struct{
	Bar[]int
}

func TestGoFunk(t *testing.T) {
	Log.InitLog()
	foo := []Foo{}
	bars := funk.Get(foo, "Bar") //panic !!
	fmt.Print(bars)
}

retrieve.go

@@ -21,7 +21,11 @@ func get(value reflect.Value, path string) reflect.Value {
 		var resultSlice reflect.Value
 
 		length := value.Len()
-
+
+		if length == 0 {
+			return resultSlice
+		}
+
 		for i := 0; i < length; i++ {
 			item := value.Index(i)