refixed "must not contain any null bytes"

Author: liborm85

src/PhpWord/Element/Image.php

@@ -454,7 +454,7 @@ private function setSourceType()
             } else {
                 $this->sourceType = self::SOURCE_GD;
             }
-        } elseif ($this->isFile($this->source)) {
+        } elseif ((strpos($this->source, chr(0)) === false) && @file_exists($this->source)) {
             $this->memoryImage = false;
             $this->sourceType = self::SOURCE_LOCAL;
         } else {
@@ -463,19 +463,6 @@ private function setSourceType()
         }
     }
 
-    /**
-     * @param string $filename
-     * @return bool
-     */
-    private function isFile($filename)
-    {
-        try {
-            return @file_exists($filename);
-        } catch (\Exception $ex) {
-            return false;
-        }
-    }
-
     /**
      * Get image size from archive
      *