Support Hunspell 1.7.0 in ispell.el

* lisp/textmodes/ispell.el
(ispell-find-hunspell-dictionaries): Invoke Hunspell with an
additional command-line argument, to work around a misfeature
in Hunspell 1.7.0 that prevents it from reporting the loaded
dictionary.  (Bug#33493)

lisp/textmodes/ispell.el

@@ -1113,7 +1113,12 @@ dictionary from that list was found."
 				 null-device
 				 t
 				 nil
-				 "-D")
+                                 ;; Hunspell 1.7.0 (and later?) won't
+                                 ;; show LOADED DICTIONARY unless
+                                 ;; there's at least one file argument
+                                 ;; on the command line.  So we feed
+                                 ;; it with the null device.
+				 "-D" null-device)
 	    (buffer-string))
 	  "[\n\r]+"
 	  t))