Antivirus heuristics detected a TrojWare.Win32.Injector.spb@281376821 in patch_gogpainkillerblack_188.8.131.52.exe. Should I be worried or this can be treated as a false alert?
Definitely false alert. Your anti-virus software is most likely freaking out due to the behavior of the patch which most AV programs think are viruses.
Feel free to run the file through Virus Total. https://www.virustotal.com/