[bugfix] Updated ```DiagnoseCommand::execute()``` and ```DiagnoseCommand::getGithubRateLimit()```

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #3859
| Doc PR        | none

Fixes #3859.

src/Composer/Command/DiagnoseCommand.php

@@ -51,6 +51,9 @@ EOT
         ;
     }
 
+    /**
+     * {@inheritdoc}
+     */
     protected function execute(InputInterface $input, OutputInterface $output)
     {
         $composer = $this->getComposer(false);
@@ -98,8 +101,9 @@ EOT
             }
         } else {
             $this->getIO()->write('Checking github.com rate limit: ', false);
+            try {
                 $rate = $this->getGithubRateLimit('github.com');
-
+                $this->outputResult(true);
                 if (10 > $rate['remaining']) {
                     $this->getIO()->write('<warning>WARNING</warning>');
                     $this->getIO()->write(sprintf(
@@ -111,8 +115,13 @@ EOT
                         $rate['remaining'],
                         $rate['limit']
                     ));
+                }
+            } catch (\Exception $e) {
+                if ($e instanceof TransportException && $e->getCode() === 401) {
+                    $this->outputResult('<comment>The oauth token for '.$domain.' seems invalid, run "composer config --global --unset github-oauth.'.$domain.'" to remove it</comment>');
                 } else {
-                $this->getIO()->write('<info>OK</info>');
+                    $this->outputResult($e);
+                }
             }
         }
 
@@ -263,25 +272,23 @@ EOT
         }
     }
 
+    /**
+     * @param string $domain
+     * @param string $token
+     * @return array
+     * @throws TransportException
+     */
     private function getGithubRateLimit($domain, $token = null)
     {
         if ($token) {
             $this->getIO()->setAuthentication($domain, $token, 'x-oauth-basic');
         }
 
-        try {
         $url = $domain === 'github.com' ? 'https://api.'.$domain.'/rate_limit' : 'https://'.$domain.'/api/rate_limit';
         $json = $this->rfs->getContents($domain, $url, false, array('retry-auth-failure' => false));
         $data = json_decode($json, true);
 
         return $data['resources']['core'];
-        } catch (\Exception $e) {
-            if ($e instanceof TransportException && $e->getCode() === 401) {
-                return '<comment>The oauth token for '.$domain.' seems invalid, run "composer config --global --unset github-oauth.'.$domain.'" to remove it</comment>';
-            }
-
-            return $e;
-        }
     }
 
     private function checkDiskSpace($config)
@@ -308,6 +315,9 @@ EOT
         return true;
     }
 
+    /**
+     * @param bool|string|\Exception $result
+     */
     private function outputResult($result)
     {
         if (true === $result) {