emacs: factor out calculation of mm-inline-override-types

The intended use case of this new function is to make reply behaviour
track that of show with respect to attachments.

Also fix the glob (which worked by fluke) into the documented regexp.

emacs/notmuch-lib.el

@@ -1037,6 +1037,14 @@ region if the region is active, or both `point' otherwise."
   'notmuch-interactive-region
   "notmuch 0.29")
 
+(defun notmuch--inline-override-types ()
+  "Override mm-inline-override-types to stop application/*
+parts from being displayed unless the user has customized
+it themselves."
+  (if (equal mm-inline-override-types
+	     (eval (car (get 'mm-inline-override-types 'standard-value))))
+      (cons "application/.*" mm-inline-override-types)
+    mm-inline-override-types))
 ;;; _
 
 (provide 'notmuch-lib)

emacs/notmuch-show.el

@@ -1264,14 +1264,8 @@ matched."
   (let ((buffer-name (generate-new-buffer-name
 		      (or buffer-name
 			  (concat "*notmuch-" thread-id "*"))))
-	;; We override mm-inline-override-types to stop application/*
+	(mm-inline-override-types (notmuch--inline-override-types)))
-	;; parts from being displayed unless the user has customized
+
-	;; it themselves.
-	(mm-inline-override-types
-	 (if (equal mm-inline-override-types
-		    (eval (car (get 'mm-inline-override-types 'standard-value))))
-	     (cons "application/*" mm-inline-override-types)
-	   mm-inline-override-types)))
     (pop-to-buffer-same-window (get-buffer-create buffer-name))
     ;; No need to track undo information for this buffer.
     (setq buffer-undo-list t)