Overflows are not detected by sscanf(), so stop using it:
* plugin-runner.c (main/parse_opt): Change from using "sscanf()" to
"strtoimax()".
* plugins.d/mandos-client.c (main/parse_opt, main): Change from using
"sscanf()" to
"strtoimax()" and
"strtof()".
* splashy.c (main): Change from using "sscanf()" to "strtoimax()".
* usplash.c (main): - '' -