pkg/cover: don't show programs when we don't have them
pkg/cover: don't show programs when we don't have them

tools/syz-cover doesn't provide any programs,
don't show counts/links to programs in such case.

xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller