Make sure kernelver array doesn't contain empty element

The shift from the `< <(cmd)` idom to `<<<"$(cmd)"` which is needed to work
without /proc being mounted has the unfortunate side effect that the exit
status of `cmd` is ignored where it wasn't before.

This can cause statements that previously always had valid input to be
called on empty strings.

One such occurrence was in `setup_kernels_arches()`, which, among other
things, populates the `kernelver` array; after the `<<<` change, this array
could contain an empty string as an element.

This commit adds a sanity check to make sure we don't pretend there is a
kernel whose version number is the empty string.

dkms.in

@@ -374,6 +374,7 @@ setup_kernels_arches()
         local i
         i=0
         while read line; do
+            [[ -n "$line" ]] || continue
             line=${line#*/}; line=${line#*/};
             # (I would leave out the delimiters in the status output
             #  in the first place.)