checks: don't panic on a DT_SONAME without .so in it

[arpitjain099]

wolfictl check so-name panics with index out of range [1] with length 1 when an ELF in the apk has a DT_SONAME that doesn't contain .so.

getSonameFiles appends the raw DT_SONAME string to the file list as-is. Unlike the filenames picked up by the regex, that string is just whatever the linker was told to put there, so libevil or badsoname are both legal and neither splits on .so. checkSonamesMatch then does strings.Split(soname, ".so")[1] in both loops and blows up.

Fix is to skip a soname with no .so in it, since there's no version to compare in that case. Both loops needed it (the existing-package one at the map build, and the new-package one below it).

Added two rows to the existing checkSonamesMatch table test covering each side. They panic before the change and pass after. go test ./pkg/checks/ is green.