pdfsig: fix use after free

It can happen that destroying the pdf tries to log, which needs
globalParams, so destroy globalParams last

Fixes issue #733
diff --git a/utils/pdfsig.cc b/utils/pdfsig.cc
index 3a432b3..6551472 100644
--- a/utils/pdfsig.cc
+++ b/utils/pdfsig.cc
@@ -276,9 +276,9 @@
   exitCode = 0;
 
 end:
-  delete globalParams;
   delete fileName;
   delete doc;
+  delete globalParams;
 
   return exitCode;
 }