[MCL-1440] Ignores -Xmx tag at will / Injects -Xmx512 at the end of JVM arguments

Crashes with :

Client> Error occurred during initialization of VM
Client> Incompatible minimum and maximum heap sizes specified
Client> Picked up _JAVA_OPTIONS: -Xmx512M
Game ended with bad state (exit code 1)
Ignoring visibility rule and showing launcher due to a game crash

Seems to appear that the Xms tag is read but the Xmx tag is ignored, meaning that Xms > Xmx, which results in the crash.

Reasons to believe this:

"Client> Picked up _JAVA_OPTIONS: -Xmx512M" in log suggests that it is forced to run with 512 MB of RAM.
Running with JVM args "-Xmx2048M -Xms512M" works fine but with "-Xmx2048M -Xms513M" still crashes.