run mpcmdrun command if the exe exists

prevents errors if disabling defender using '--force' on an already disabled environment. why? sometimes our defender package doesn't get removed when enabling Defender and reinstalling the package fixes it

Author: melo936

common/lib/src/services/security_service.dart

@@ -261,8 +261,10 @@ class SecurityService implements SetupService {
       await _shell.run(
           'start /WAIT /MIN /B "" "%systemroot%\\System32\\gpupdate.exe" /Target:Computer /Force');
 
-      await _shell.run(
-          "PowerShell -EP Unrestricted -NonInteractive -NoLogo -NoP -C 'Start-Process -FilePath \"$_mpCmdRunString\" -ArgumentList \"-RemoveDefinitions -All\" -NoNewWindow -Wait'");
+      if (await File(_mpCmdRunString).exists()) {
+        await _shell.run(
+            "PowerShell -EP Unrestricted -NonInteractive -NoLogo -NoP -C 'Start-Process -FilePath \"$_mpCmdRunString\" -ArgumentList \"-RemoveDefinitions -All\" -NoNewWindow -Wait'");
+      }
 
       await _shell.run(
           '"$directoryExe\\MinSudo.exe" --NoLogo --TrustedInstaller reg add "HKLM\\SOFTWARE\\Microsoft\\Windows Defender" /v DisableAntiSpyware /t REG_DWORD /d 1 /f');