zsh:keys:ratio_dots: Fix preview of first word

Previously the path preview misbehaved when typing dots on the first
shell word (e.g. executing a script in a parent directory). This
happened as the `(z)` parameter expansion flag does not expand to an
array rather a scalar. Because of that, `[-1]` returns the last
character.

Work around this issue by prepending LBUFFER with a dummy word, so that
it always contains at least 2 words.

.config/zsh/zshrc.d/60-keys.zsh

@@ -100,9 +100,13 @@ function rationalize_dots {
 		return
 	fi
 
+	# NOTE: This is a hack to fix the (z) expansion flag if the path is the only
+	#       word in LBUFFER, as then [:-1] treats the expansion as a scalar and
+	#       returns the last character (i.e. always `/`).
+	local lbuffer_words="x $LBUFFER"
 	# Print currently typed path as absolute path with "collapsed"/reversed
 	# filename expansion.
-	zle -M "${(D)${(z)LBUFFER}[-1]:a}"
+	zle -M "${(D)${(z)lbuffer_words}[-1]:a}"
 }
 zle -N rationalize_dots
 bindkey . rationalize_dots