Fixed problems with svg_load_image -- no more crashes (hopefully)

* src/image.c (svg_load): Watch out for nil value of current buffer's
filename.  Re-enable filename thing for not-a-file case.
Add missing ChangeLog entry for prior commit.
load-history may contain nil "filenames"

* lisp/emacs-lisp/package.el (package--list-loaded-files): Handle
`(nil ...)' elements in `load-history'.
* src/keyboard.c (swallow_events): Don't redisplay if there's input pending.