fix: when no body supplied, do not set bodyUsed to true

fetch.js

@@ -162,6 +162,7 @@ if (support.iterable) {
 }
 
 function consumed(body) {
+  if (body._noBody) return
   if (body.bodyUsed) {
     return Promise.reject(new TypeError('Already read'))
   }
@@ -231,6 +232,7 @@ function Body() {
     this.bodyUsed = this.bodyUsed
     this._bodyInit = body
     if (!body) {
+      this._noBody = true;
       this._bodyText = ''
     } else if (typeof body === 'string') {
       this._bodyText = body

test/test.js

@@ -996,6 +996,15 @@ exercise.forEach(function(exerciseMode) {
               assert(error instanceof TypeError, 'Promise rejected after body consumed')
             })
         })
+
+        test('does not set bodyUsed to true if no body supplied', function() {
+          var response = new Response();
+          assert(response.text, 'Body does not implement text')
+          assert.equal(response.bodyUsed, false)
+          response.text()
+          assert.equal(response.bodyUsed, false)
+          return response.text()
+        })
       })
     })