Filled out implementation of check_client function

includes/check_input.hpp

@@ -17,6 +17,7 @@ typedef struct {
 
 /* This function checks the IP address and port passed to it, and returns a struct,
 that contains information about the game mode, and contains the server socket.
+It assumes that both ip_text and port_text are non-null
 TODO - Add better error checking. */
 GameType check_server(char* ip_text, char* port_text);