Duplicate entries in PATH environment variable

[AndrewMusser]

Describe the bug

Each time lpm-setup.exe is run, it adds an entry to the SYSTEM environment variable called PATH that points back to the location of lpm.cmd. Is the setup is run multiple times, duplicate entries are created in the PATH variable.

To reproduce

Run the lpm-setup.exe installer multiple times.

Expected behavior

The installer should check for an existing entry, and not add a new one if it already exists.

Additional information

Priority: High
Happens on v1.0.3 (and all prior).