Make package-install-from-buffer not move point

* lisp/emacs-lisp/package.el (package-install-from-buffer):
Use save-excursion here (bug#22616).

lisp/emacs-lisp/package.el

@@ -1989,7 +1989,8 @@ Downloads and installs required packages as needed."
             ((derived-mode-p 'tar-mode)
              (package-tar-file-info))
             (t
-             (package-buffer-info))))
+             (save-excursion
+              (package-buffer-info)))))
          (name (package-desc-name pkg-desc)))
     ;; Download and install the dependencies.
     (let* ((requires (package-desc-reqs pkg-desc))