FIX louietan#76: handle both old and new function signatures of `request--curl-callback'

'request.el' commit '8ccbae1b5e5e2ae68112dd46a6bee67d318b0deb' changed the
function signature ("arity") from 2 to 3 arguments. The current stable version
of that package still uses the old number of args. The rolling-release master
branch of 'request.el' uses the new number of args. This function handles both
cases for the time being.

(It is generally frowned upon to use provate functions from other packages since
they are not considered a stable interface. However, for now, it is unavoidable
since there is no "stable" interface to forec 'request.el' to run the callback.)

Author: Sodel-the-Vociferous

anki-editor.el

@@ -147,9 +147,10 @@ See https://apps.ankiweb.net/docs/manual.html#latex-conflicts.")
         (json-array-type 'list)
         reply err)
 
-    (let ((response (request (format "http://%s:%s"
-                                     anki-editor-anki-connect-listening-address
-                                     anki-editor-anki-connect-listening-port)
+    (let* ((url (format "http://%s:%s"
+                        anki-editor-anki-connect-listening-address
+                        anki-editor-anki-connect-listening-port))
+           (response (request url
                              :type "POST"
                              :parser 'json-read
                              :data request-body
@@ -164,7 +165,15 @@ See https://apps.ankiweb.net/docs/manual.html#latex-conflicts.")
       ;; might not be called right away but at a later time, that's
       ;; why here we manually invoke callbacks to receive the result.
       (unless (request-response-done-p response)
-        (request--curl-callback (get-buffer-process (request-response--buffer response)) "finished\n")))
+        ;; (request--curl-callback "localhost" (get-buffer-process (request-response--buffer response)) "finished\n")))
+        (if (= 2 (func-arity (function 'request--curl-callback)))
+            ;; Handle the older, stable version of 'request.el' in which
+            ;; `request--curl-callback' has two args.
+            (request--curl-callback (get-buffer-process (request-response--buffer response)) "finished\n")
+          ;; Handle new 3-argument function signature as of 'request.el' commit
+          ;; '8ccbae1b5e5e2ae68112dd46a6bee67d318b0deb'. Should fix anki-editor
+          ;; errors for those using newer versions of 'request.el'.
+          (request--curl-callback url (get-buffer-process (request-response--buffer response)) "finished\n"))))
 
     (when err (error "Error communicating with AnkiConnect using cURL: %s" err))
     (or reply (error "Got empty reply from AnkiConnect"))))