Do not try to read document protection if not present

src/PhpWord/Reader/Word2007/AbstractPart.php

@@ -588,6 +588,8 @@ abstract class AbstractPart
                     return $possibleAttribute;
                 }
             }
+
+            return null;
         }
 
         return $attributes;

src/PhpWord/Reader/Word2007/Settings.php

@@ -109,8 +109,10 @@ class Settings extends AbstractPart
         $documentProtection = $phpWord->getSettings()->getDocumentProtection();
 
         $edit = $xmlReader->getAttribute('w:edit', $node);
+        if ($edit !== null) {
             $documentProtection->setEditing($edit);
         }
+    }
 
     /**
      * Sets the proof state