Let PdfFileMerger open the files to be merged itself

Before, the files were closed before actually being processed by PdfFileMerger

cms/service/PrintingService.py

@@ -21,6 +21,7 @@
 
 """
 
+import contextlib
 import cups
 import logging
 import os
@@ -189,14 +190,11 @@ def execute(self, entry):
                     "Failed to create title page with command: %s"
                     "(error %d)" % (pretty_print_cmdline(cmd), ret))
 
-            pdfmerger = PdfFileMerger()
-            with open(title_pdf, "rb") as file_:
-                pdfmerger.append(file_)
-            with open(source_pdf, "rb") as file_:
-                pdfmerger.append(file_)
-            result = os.path.join(directory, "document.pdf")
-            with open(result, "wb") as file_:
-                pdfmerger.write(file_)
+            with contextlib.closing(PdfFileMerger()) as pdfmerger:
+                pdfmerger.append(title_pdf)
+                pdfmerger.append(source_pdf)
+                result = os.path.join(directory, "document.pdf")
+                pdfmerger.write(result)
 
             try:
                 printer_connection = cups.Connection()