Fix error handling for pdfs whose info cannot be read

scripts/pdf_unlock.py

@@ -116,8 +116,12 @@ def pdf_unlock(pdf_file, overwrite=False):
         return
 
     # Skip file if it is not encrypted
+    try:
         if not isencrypted(pdf_file):
             return
+    # SKip file if pdf info cannot be read
+    except AttributeError:
+        return
 
     # Get name of Ghostscript executable
     if os.sys.platform == 'win32':