Fix remote code execution #1

[0x27]

Passing unsanitized user input into the shell_exec function leads to remote code execution.

In this instance, to execute the id command, one would send a request such as the following:

GET /tilt.php?position=;id

Checking history, a similar issue was previously reported

A similar issue also exists in this file, however I am leaving fixing that as a learning exercise for you.