Throw InvalidArgumentException in case getint4d fails

Classes/PHPExcel/Shared/OLERead.php

@@ -306,6 +306,34 @@ private static function getInt4d($data, $pos)
         // FIX: represent numbers correctly on 64-bit system
         // http://sourceforge.net/tracker/index.php?func=detail&aid=1487372&group_id=99160&atid=623334
         // Hacked by Andreas Rehm 2006 to ensure correct result of the <<24 block on 32 and 64bit systems
+
+        // Handling Errors : Dependancy of code on $pos of $data. Hence added a check to make sure the block is valid/readable.
+        // Throwing Exception incase of any error.
+
+        if (!isset($data[$pos + 3])) {
+            //String $error_message : Declaration only once
+            $error_message = 'EXCEPTION (InvalidBlockException) :: CORRUPT BLOCKS IN XLS FILE'."\nCallStack:\n";
+
+            foreach (debug_backtrace() as $arr_info_element) {
+                //String $message : Redeclaration
+                $message = '';
+
+                foreach ($arr_info_element as $info_property => $info_value) {
+                    // ignoring the properties [object], [args] and [type] as it causes essay effect while printing error message.
+                    if ($info_property == 'object' || $info_property == 'args' || $info_property == 'type') {
+                        continue;
+                    }
+
+                    $message .= $info_property.'=>['.$info_value.'] ';
+                }
+
+                //add error message
+                if (!empty($message)) {
+                    $error_message .= $message."\n";
+                }
+            }
+            throw new InvalidArgumentException($error_message);       
+        }
         $_or_24 = ord($data[$pos + 3]);
         if ($_or_24 >= 128) {
             // negative number