fix: check for existence of unref before calling

Environments like Electron do not always expose the Node.js setTiemout,
so there is no unref function on resTimeout. So update the check to also
check if the unref function exists

Ref: electron/electron#21162

PR-URL: #13
Credit: @ewanharris
Close: #13
Reviewed-by: @isaacs

lib/body.js

@@ -132,7 +132,7 @@ class Body {
 
     // do not keep the process open just for this timeout, even
     // though we expect it'll get cleared eventually.
-    if (resTimeout) {
+    if (resTimeout && resTimeout.unref) {
       resTimeout.unref()
     }
 

test/body.js

@@ -231,6 +231,20 @@ t.test('json', async t => {
   })
 })
 
+t.test('handles environments where setTimeout does not have unref', async t => {
+  const originalSetTimeout = setTimeout
+  // simulate environments without unref()
+  global.setTimeout = (func, time) =>
+    Object.assign(originalSetTimeout(func, time), { unref: null })
+  t.teardown(() => global.setTimeout = originalSetTimeout)
+
+  t.doesNotThrow(async () => {
+    const b = new Body(new Blob('a=1'), { timeout: 100 })
+    await b.text()
+    t.end()
+  })
+})
+
 t.test('write to streams', async t => {
   const w = body => Body.writeToStream(
     new Minipass({ encoding: 'utf8' }),