MemoryLimit: rewrite for PHP 7.1+

fixes #1222

library/Director/Application/MemoryLimit.php

@@ -33,9 +33,10 @@ class MemoryLimit
     public static function parsePhpIniByteString($string)
     {
         $val = trim($string);
-        $last = strtoupper(substr($val, -1, 1));
 
-        switch ($last) {
+        if (preg_match('/^(\d+)([KMG])$/', $val, $m)) {
+            $val = $m[1];
+            switch ($m[2]) {
                 case 'G':
                     $val *= 1024;
                 // Intentional fall-through
@@ -45,6 +46,7 @@ class MemoryLimit
                 case 'K':
                     $val *= 1024;
             }
+        }
 
         return intval($val);
     }