Merge #3285

3285: Fix invalid server-assigned utf8 names with (1) prefix (fixes #3269) r=heinrich5991 a=def-

## Checklist

- [ ] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test if it works standalone, system.c especially
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: def <dennis@felsin9.de>

src/engine/server/server.cpp

@@ -394,7 +394,9 @@ bool CServer::SetClientNameImpl(int ClientID, const char *pNameRequest, bool Set
 		// auto rename
 		for(int i = 1;; i++)
 		{
-			str_format(aNameTry, sizeof(aNameTry), "(%d)%s", i, aTrimmedName);
+			char aNameTryBrokenEnd[MAX_NAME_LENGTH];
+			str_format(aNameTryBrokenEnd, sizeof(aNameTryBrokenEnd), "(%d)%s", i, aTrimmedName);
+			str_utf8_copy(aNameTry, aNameTryBrokenEnd, sizeof(aNameTry));
 			if(IsClientNameAvailable(ClientID, aNameTry))
 				break;
 		}