Fixes #12: sbasm exit code = 0 when error is not fatal?

[wil-low]

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Please check if I missed something, just wanted a quick fix to use sbasm in makefile properly ;)

[sbprojects]

Thanks for spotting this one. I've made a slightly different change and will commit that instead of your pull request. Your change comes after a possible run command. And I think the run command should not be executed when there was an error. See: https://www.sbprojects.net/sbasm/directives.php?directive=ru

[wil-low]

Great, thank you!