Fix deprecation on stropos() usage on sfDebug::shortenFilePath (#299)

Fix PHP v8.x deprecation on strpos() usage with `null` as first parameter

Author: iricketson

lib/debug/sfDebug.class.php

@@ -235,6 +235,10 @@ public static function removeObjects($values)
      */
     public static function shortenFilePath($file)
     {
+        if (!$file) {
+            return $file;
+        }
+
         foreach (array('sf_root_dir', 'sf_symfony_lib_dir') as $key) {
             if (0 === strpos($file, $value = sfConfig::get($key))) {
                 $file = str_replace($value, strtoupper($key), $file);

test/unit/debug/sfDebugTest.php

@@ -10,10 +10,13 @@
 
 require_once __DIR__.'/../../bootstrap/unit.php';
 
-$t = new lime_test(1);
+$t = new lime_test(2);
 
 // ::removeObjects()
 $t->diag('::removeObjects()');
 $objectArray = array('foo', 42, new sfDebug(), array('bar', 23, new lime_test(null)));
 $cleanedArray = array('foo', 42, 'sfDebug Object()', array('bar', 23, 'lime_test Object()'));
 $t->is_deeply(sfDebug::removeObjects($objectArray), $cleanedArray, '::removeObjects() converts objects to String representations using the class name');
+
+$t->diag('::shortenFilePath()');
+$t->is(sfDebug::shortenFilePath(null), null, '->shortenFilePath() handles a null value');