Issue #6050: Don't fail extracting a directory from a zipfile if
the directory already exists.
diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index e3d40b4..68885f9 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -971,7 +971,8 @@
             os.makedirs(upperdirs)
 
         if member.filename[-1] == '/':
-            os.mkdir(targetpath)
+            if not os.path.isdir(targetpath):
+                os.mkdir(targetpath)
             return targetpath
 
         source = self.open(member, pwd=pwd)