Initialize dlSz to avoid NameError when transfer fails

Author: matyasselmeci

bin/stashcp

@@ -199,6 +199,8 @@ def doStashCpSingle(sourceFile, destination, debug=False):
     xrd_exit=timed_transfer(filename=sourceFile, debug=debug, destination=destination)
 
     end2=int(time.time()*1000)
+
+    dlSz=0
     if os.path.exists(destination):
         dlSz=os.stat(destination).st_size
     destSpace=1