Fix error handling for pdfs whose info cannot be read

scripts/pdf_unlock.py

@@ -116,7 +116,11 @@ def pdf_unlock(pdf_file, overwrite=False):
         return
 
     # Skip file if it is not encrypted
-    if not isencrypted(pdf_file):
+    try:
+        if not isencrypted(pdf_file):
+            return
+    # SKip file if pdf info cannot be read
+    except AttributeError:
         return
 
     # Get name of Ghostscript executable