modify show test helper to work around BSD quirk

The BSD `seq` command handles `seq 0` weird.

tests/test_functions/show.fish

@@ -4,9 +4,13 @@ function show --no-scope-shadowing
         if set -q $v
             set -l c (count $$v)
             printf '$%s count=%d\n' $v $c
+            # This test is to work around a bogosity of the BSD `seq` command. If called with
+            # `seq 0` it emits `1`, `0`. Whereas that GNU version outputs nothing.
+            if test $c -gt 0
                 for i in (seq $c)
                     printf '$%s[%d]=|%s|\n' $v $i $$v[1][$i]
                 end
+            end
         else
             echo \$$v is not set
         end