Fix false positives in checkResourceUrl()

Without this proposed fix, I'm receiving false errors about the CiviCRM Resource URL not being set correctly.

The stripos() function will return '0' if the needle string is the first thing found in the haystack. Thus, you must use equivalence rather than a true/false test where "position zero" evaluates to false.

Tested on Civi 5.3.0 on WordPress 4.9.7

I can access http://coastaltrails.org/wp-content/plugins/civicrm/civicrm/packages/jquery/css/images/arrow.png But WITHOUT the fix, I get an error
```
The Resource URL is not set correctly. Please set the CiviCRM Resource URL.
```
I have CiviCRM Resource URL set to `[civicrm.root]/`

My URL Variables are calculated as:
```
[cms.root]	http://coastaltrails.org/
[civicrm.root]	http://coastaltrails.org/wp-content/plugins/civicrm/civicrm/
[civicrm.files]	http://coastaltrails.org/wp-content/uploads/civicrm/
These variables are computed automatically using civicrm.settings.php and its options, such as CIVICRM_TEMPLATE_COMPILEDIR.
```

diff --git a/CRM/Utils/Check/Component/Env.php b/CRM/Utils/Check/Component/Env.php
index df866185edcdd1d597856354eb4b9c9bc67f524a..a253716e42f30e6b639bcb4157153a31006d8be1 100644 (file)
--- a/CRM/Utils/Check/Component/Env.php
+++ b/CRM/Utils/Check/Component/Env.php
@@ -910,7 +910,7 @@ class CRM_Utils_Check_Component_Env extends CRM_Utils_Check_Component {
     $arrowUrl = CRM_Core_Config::singleton()->userFrameworkResourceURL . 'packages/jquery/css/images/arrow.png';
     $headers = get_headers($arrowUrl);
     $fileExists = stripos($headers[0], "200 OK") ? 1 : 0;
-    if (!$fileExists) {
+    if ($fileExists === FALSE) {
       $messages[] = new CRM_Utils_Check_Message(
         __FUNCTION__,
         ts('The Resource URL is not set correctly. Please set the <a href="%1">CiviCRM Resource URL</a>.',