Don’t err in pip-frame-remove-buffer if there is no PIP frame

This is useful e.g. to prevent the error when a PIP frame with a
temporarily displayed buffer is deleted before the buffer timer
attempts to remove the buffer.

README.org

@@ -43,6 +43,26 @@ this utility:
 
 * How?
 
+** Installation
+
+You can install pip-frame.el from [[https://melpa.org/#/pip-frame][MELPA]].  If you use [[https://github.com/radian-software/straight.el][straight.el]] and
+prefer using source repos directly, you can install pip-frame.el as
+follows:
+
+   #+begin_src elisp
+(straight-use-package
+ '(pip-frame :type git
+             :repo "https://git.zamazal.org/pdm/pip-frame"
+             :local-repo "pip-frame"))
+   #+end_src
+
+For manual installation, simply put [[./pip-frame.el][pip-frame.el]] file to your
+=site-lisp= directory and add the following to your Emacs configuration:
+
+   #+begin_src elisp
+(require ’pip-frame)
+   #+end_src
+
 ** Commands
 
 The PIP frame is created using =M-x pip-frame-add-buffer= command.  You

pip-frame.el

@@ -3,7 +3,8 @@
 ;; Copyright (C) 2022 Milan Zamazal <pdm@zamazal.org>
 
 ;; Author: Milan Zamazal <pdm@zamazal.org>
-;; Package-Version: 1
+;; Version: 1
+;; Package-Requires: ((emacs "25.1"))
 ;; Keywords: frames
 ;; URL: https://git.zamazal.org/pdm/pip-frame
 
@@ -32,6 +33,8 @@
 ;; `M-x pip-frame-remove-buffer' or close the whole frame with
 ;; `M-x pip-frame-delete-frame'.
 
+;;; Code:
+
 (require 'cl-lib)
 
 (defgroup pip-frame ()
@@ -58,6 +61,7 @@ Usually, the value should be larger than 0 and much smaller than 1."
 (defcustom pip-frame-parameters
   '((left . 0.9)
     (top .  0.9)
+    (tab-bar-lines . 0)
     (minibuffer . nil))
   "Alist of frame parameters to use for the PIP frame.
 The frame size is determined automatically using `pip-frame-scale'
@@ -171,7 +175,8 @@ If the buffer is not present in the PIP frame, do nothing."
   (interactive (list (completing-read "Remove PIP buffer: "
                                       (mapcar #'buffer-name (pip-frame--buffers))
                                       nil t)))
-  (let* ((windows (window-list (pip-frame--get-frame)))
+  (if-let ((frame (pip-frame--get-frame t))
+           (windows (window-list frame))
            (buffer (get-buffer buffer-or-name))
            (windows-to-delete (cl-remove buffer windows
                                          :key #'window-buffer
@@ -192,18 +197,22 @@ If the buffer is not present in the PIP frame, do nothing."
       (round (* pip-frame-move-step (nth (if vertical 3 2) workarea))))))
 
 (defun pip-frame-move-left ()
+  "Move the PIP frame left."
   (interactive)
   (pip-frame--move (- (pip-frame--move-step nil)) 0))
 
 (defun pip-frame-move-right ()
+  "Move the PIP frame right."
   (interactive)
   (pip-frame--move (pip-frame--move-step nil) 0))
 
 (defun pip-frame-move-up ()
+  "Move the PIP frame up."
   (interactive)
   (pip-frame--move 0 (- (pip-frame--move-step t))))
 
 (defun pip-frame-move-down ()
+  "Move the PIP frame down."
   (interactive)
   (pip-frame--move 0 (pip-frame--move-step t)))
 
@@ -224,3 +233,9 @@ Any other key stops this command and executes its own command."
   (set-transient-map pip-frame-move-map t))
 
 (provide 'pip-frame)
+
+;; Local Variables:
+;; checkdoc-force-docstrings-flag: nil
+;; End:
+
+;;; pip-frame.el ends here