fix ctx.body= content-type override check. Thanks @jonathanong

lib/context.js

@@ -153,8 +153,6 @@ module.exports = {
   set body(val) {
     this._body = val;
 
-    if (this.type) return;
-
     // no content
     if (null == val) {
       var s = this.status;
@@ -165,6 +163,9 @@ module.exports = {
       return;
     }
 
+    // content-type already set
+    if (this.responseHeader['content-type']) return;
+
     // string
     if ('string' == typeof val) {
       this.type = ~val.indexOf('<') ? 'html' : 'text';

test/context.js

@@ -22,6 +22,15 @@ function context(req, res) {
 }
 
 describe('ctx.body=', function(){
+  describe('when Content-Type is set', function(){
+    it('should not override', function(){
+      var ctx = context();
+      ctx.type = 'png';
+      ctx.body = new Buffer('something');
+      assert('image/png' == ctx.responseHeader['content-type']);
+    })
+  })
+
   describe('when a string is given', function(){
     it('should default to text', function(){
       var ctx = context();