master f566795: Give better error messages in image-convert

[Lars Ingebrigtsen]

branch: master
commit f5667953f73b557b4461677df9a1a0017ff46f60
Author: Lars Ingebrigtsen <address@hidden>
Commit: Lars Ingebrigtsen <address@hidden>

    Give better error messages in image-convert
    
    * lisp/image/image-converter.el (image-convert): Make
    image-convert bug out earlier on a wrong IMAGE-FORMAT value
    (bug#38310).
---
 lisp/image/image-converter.el | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lisp/image/image-converter.el b/lisp/image/image-converter.el
index b4d10c8..1230b6b 100644
--- a/lisp/image/image-converter.el
+++ b/lisp/image/image-converter.el
@@ -87,6 +87,9 @@ data is returned as a string."
     (image-converter--find-converter))
   (unless image-converter
     (error "No external image converters available"))
+  (when (and image-format
+             (not (= (length (split-string (symbol-name image-format) "/")) 
2)))
+    (error "IMAGE-FORMAT should be a symbol like `image/png'"))
   (with-temp-buffer
     (set-buffer-multibyte nil)
     (when-let ((err (image-converter--convert