doc: clarify server behavior for invalid 'want' lines in HTTP protocol

Update the documentation to clearly describe how the server responds when a
client sends an invalid or malformed `want` line during the HTTP protocol
exchange. This improves understanding of Git’s behavior when handling
incorrect object requests and helps developers detect and handle such
protocol issues accurately.

Signed-off-by: Queen Ediri Jessa <qjessa662@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: QueenJcloud

Documentation/gitprotocol-http.adoc

@@ -443,7 +443,10 @@ If no "want" objects are received, send an error:
 TODO: Define error if no "want" lines are requested.
 
 If any "want" object is not reachable, send an error:
-TODO: Define error if an invalid "want" is requested.
+When a Git server receives an invalid or malformed `want` line, it
+responds with an error message that includes the offending object name.
+This clarifies the expected behavior for Git implementations and helps
+clients detect protocol issues accurately during fetch operations.
 
 Create an empty list, `s_common`.