Fix fzf's ssh host completion under failglob in bash

fzf's completion.bash globs ~/.ssh/config.d/* when listing hosts
=> With `shopt -s failglob`, a missing or empty folder makes this
   an expansion error, printing "bash: no match" on every <Tab>
   after `ssh`

Define __fzf_list_hosts before sourcing fzf, using its override
hook with bash-completion's host list, as fzf itself suggests

.bash_completion

@@ -16,6 +16,17 @@ complete -W '--quieter' generate-shell-completions
 #
 # Must be sourced before `complete_alias` below,
 # which then saves fzf's wrappers as the vanilla completions
+#
+# fzf's own host list globs ~/.ssh/config.d/*,
+# which aborts under `failglob` if that folder is empty or missing
+# => Use fzf's override hook with `bash-completion`'s host list instead
+
+__fzf_list_hosts() {
+    local COMPREPLY=()
+    _known_hosts_real ''
+    printf '%s\n' "${COMPREPLY[@]}" | command sort -u --version-sort
+}
+
 if [ -r /usr/share/doc/fzf/examples/completion.bash ]; then
     . /usr/share/doc/fzf/examples/completion.bash
 fi