Fix random sha1 in error message in http-fetch and http-push

When a downloaded ref doesn't contain a sha1, the error message displays
a random sha1 because of uninitialized memory. This happens when cloning
a repository that is already a clone of another one, in which case
refs/remotes/origin/HEAD is a symref.

Signed-off-by: Mike Hommey <mh@glandium.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http-push.c

@@ -1149,9 +1149,10 @@ int fetch_ref(char *ref, unsigned char *sha1)
 		return error("Unable to start request");
 	}
 
+	if (buffer.posn != 41)
+		return 1;
         hex[40] = '\0';
-        get_sha1_hex(hex, sha1);
-        return 0;
+	return get_sha1_hex(hex, sha1);
 }
 
 static void one_remote_object(const char *hex)

http-walker.c

@@ -986,9 +986,10 @@ static int fetch_ref(struct walker *walker, char *ref, unsigned char *sha1)
 		return error("Unable to start request");
 	}
 
+	if (buffer.posn != 41)
+		return 1;
         hex[40] = '\0';
-        get_sha1_hex(hex, sha1);
-        return 0;
+	return get_sha1_hex(hex, sha1);
 }
 
 static void cleanup(struct walker *walker)