GitHub Issue #546: Received a fatal because mb_substr was not found.

Added logic to wrap the extension missing fatal error and ensured the mb_filter function is taken from PHP base namespace and not from the FB SDK namespace.

Test running and succeeded:

PHPUnit 4.8.21 by Sebastian Bergmann and contributors.

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Time: 6.36 seconds, Memory: 12.00Mb

OK (267 tests, 614 assertions)

Author: DragonBe

src/Facebook/PseudoRandomString/PseudoRandomStringGeneratorTrait.php

@@ -48,11 +48,15 @@ public function validateLength($length)
      *
      * @param string $binaryData The binary data to convert to hex.
      * @param int    $length     The length of the string to return.
+     * @throws \RuntimeException Throws an exception when multibyte support is not enabled
      *
      * @return string
      */
     public function binToHex($binaryData, $length)
     {
-        return mb_substr(bin2hex($binaryData), 0, $length);
+        if(true !== extension_loaded('mbstring')) { 
+            throw new \RuntimeException('Multibyte support required'); 
+        }
+        return \mb_substr(\bin2hex($binaryData), 0, $length);
     }
 }