Ok, I finally got it. The approach with empty argument works well with "-i" option, when you should do not care about processes merging, Without "-i" option it is possible to add ":0" suffix to *.geany file. All workarounds do not cover a case with *.geany argument, representing non-existing file, and '-i' option is not specified. But in my case (using Geany as $EDITOR), I does not have such case.