Fix server ping never timing out when out of range gamemode is returned by server (#11556)

Co-authored-by: 1ue999 <1ue999owo@gmail.com>

core/src/mindustry/net/NetworkIO.java

@@ -130,7 +130,8 @@ public class NetworkIO{
         int version = buffer.getInt();
         String vertype = readString(buffer);
 
-        Gamemode gamemode = Gamemode.all[buffer.get()];
+        byte mode = buffer.get();
+        Gamemode gamemode = Gamemode.all[mode < Gamemode.all.length ? mode : 0];
         int limit = buffer.getInt();
 
         String description = readString(buffer);