bpo-36742: Corrects fix to handle decomposition in usernames (#13812)

diff --git a/Lib/urllib/parse.py b/Lib/urllib/parse.py
index daefb20..b660878 100644
--- a/Lib/urllib/parse.py
+++ b/Lib/urllib/parse.py
@@ -402,9 +402,9 @@
     # looking for characters like \u2100 that expand to 'a/c'
     # IDNA uses NFKC equivalence, so normalize for this check
     import unicodedata
-    n = netloc.rpartition('@')[2] # ignore anything to the left of '@'
-    n = n.replace(':', '')        # ignore characters already included
-    n = n.replace('#', '')        # but not the surrounding text
+    n = netloc.replace('@', '')   # ignore characters already included
+    n = n.replace(':', '')        # but not the surrounding text
+    n = n.replace('#', '')
     n = n.replace('?', '')
     netloc2 = unicodedata.normalize('NFKC', n)
     if n == netloc2: