(feature): make org-roam-insert work in org-capture buffers (#134)

In org-capture buffers, (buffer-file-name) will always return nil. But
we can get the name of the buffer that we are capturing into
via (buffer-base-buffer), then getting the path to the current file
works as expected.

org-roam.el

@@ -287,7 +287,8 @@ If PREFIX, downcase the title before insertion."
          (title (completing-read "File: " completions))
          (absolute-file-path (or (cadr (assoc title completions))
                                  (org-roam--make-new-file-path (org-roam--get-new-id title) t)))
-         (current-file-path (-> (current-buffer)
+         (current-file-path (-> (or (buffer-base-buffer)
+                                    (current-buffer))
                                 (buffer-file-name)
                                 (file-truename)
                                 (file-name-directory))))