Don't rely on PHP_INT_MIN if it isn't defined (PHP < 7).

Author: pocketarc

src/FontLib/BinaryStream.php

@@ -274,8 +274,11 @@ public function writeFixed($data) {
   public function readLongDateTime() {
     $this->readUInt32(); // ignored
     $date = $this->readUInt32() - 2082844800;
+    
+    # PHP_INT_MIN isn't defined in PHP < 7.0
+    $php_int_min = defined("PHP_INT_MIN") ? PHP_INT_MIN : ~PHP_INT_MAX;
 
-    if (is_string($date) || $date > PHP_INT_MAX || $date < PHP_INT_MIN) {
+    if (is_string($date) || $date > PHP_INT_MAX || $date < $php_int_min) {
       $date = 0;
     }