chore: remove else instead of return/continue (#1502)

As[ Effective Go](https://golang.org/doc/effective_go.html?#if) about `if` said, remove else statement instead of return/continue statement.

binding/form_mapping.go

@@ -74,16 +74,16 @@ func mapForm(ptr interface{}, form map[string][]string) error {
 				}
 			}
 			val.Field(i).Set(slice)
-		} else {
-			if _, isTime := structField.Interface().(time.Time); isTime {
-				if err := setTimeField(inputValue[0], typeField, structField); err != nil {
-					return err
-				}
-				continue
-			}
-			if err := setWithProperType(typeField.Type.Kind(), inputValue[0], structField); err != nil {
+			continue
+		}
+		if _, isTime := structField.Interface().(time.Time); isTime {
+			if err := setTimeField(inputValue[0], typeField, structField); err != nil {
 				return err
 			}
+			continue
+		}
+		if err := setWithProperType(typeField.Type.Kind(), inputValue[0], structField); err != nil {
+			return err
 		}
 	}
 	return nil

context.go

@@ -665,9 +665,9 @@ func (c *Context) Status(code int) {
 func (c *Context) Header(key, value string) {
 	if value == "" {
 		c.Writer.Header().Del(key)
-	} else {
-		c.Writer.Header().Set(key, value)
+		return
 	}
+	c.Writer.Header().Set(key, value)
 }
 
 // GetHeader returns value from request headers.
@@ -755,9 +755,9 @@ func (c *Context) JSONP(code int, obj interface{}) {
 	callback := c.DefaultQuery("callback", "")
 	if callback == "" {
 		c.Render(code, render.JSON{Data: obj})
-	} else {
-		c.Render(code, render.JsonpJSON{Callback: callback, Data: obj})
+		return
 	}
+	c.Render(code, render.JsonpJSON{Callback: callback, Data: obj})
 }
 
 // JSON serializes the given struct as JSON into the response body.

render/json.go

@@ -128,10 +128,8 @@ func (r AsciiJSON) Render(w http.ResponseWriter) (err error) {
 
 	var buffer bytes.Buffer
 	for _, r := range string(ret) {
-		cvt := ""
-		if r < 128 {
-			cvt = string(r)
-		} else {
+		cvt := string(r)
+		if r >= 128 {
 			cvt = fmt.Sprintf("\\u%04x", int64(r))
 		}
 		buffer.WriteString(cvt)