[BUG] ChangeUserPassword throws NPE before its null check when player is missing #973

Discovered during #918.

In src/main/java/servlets/admin/userManagement/ChangeUserPassword.java:

String player = (String) request.getParameter("player");
log.debug("player = " + player.toString());
...
notNull = (player != null) && (newPassword != null);

If the player parameter is missing, player.toString() throws a NullPointerException before the null check. The generic catch (Exception e) swallows it and returns "An error Occurred! Please try again.", so the "Null values detected" / "Invalid Request" branch can never run for a missing player.

Fix: log player without calling .toString() (string concatenation already handles null), and add a test that posts without player and expects the "Invalid Request" response.