Fix internal server error when updating 3pid address with invalid email (#18125)

When updating 3pid for a user email from admin api and sending invalid
email the server throws 500 internal server error.
changed to 400 Bad request and returned the error message

Signed-off-by: qashlan <ahmedelqashlan@gmail.com>
Signed-off-by: Ahmed Qashlan <ahmedelqashlan@gmail.com>

changelog.d/18125.bugfix

@@ -0,0 +1 @@
+Fix a bug when updating a user 3pid with invalid returns 500 server error change to 400 with a message.

synapse/handlers/auth.py

@@ -1579,7 +1579,10 @@ class AuthHandler:
         # for the presence of an email address during password reset was
         # case sensitive).
         if medium == "email":
-            address = canonicalise_email(address)
+            try:
+                address = canonicalise_email(address)
+            except ValueError as e:
+                raise SynapseError(400, str(e))
 
         await self.store.user_add_threepid(
             user_id, medium, address, validated_at, self.hs.get_clock().time_msec()
@@ -1610,7 +1613,10 @@ class AuthHandler:
         """
         # 'Canonicalise' email addresses as per above
         if medium == "email":
-            address = canonicalise_email(address)
+            try:
+                address = canonicalise_email(address)
+            except ValueError as e:
+                raise SynapseError(400, str(e))
 
         await self.store.user_delete_threepid(user_id, medium, address)