Revert slurp_image extraction for svg_load

* src/image.c (svg_load): Inline slurp_image code again, as it didn't
build in its current form.
Reported by Andreas Schwab <schwab@linux-m68k.org>.

src/image.c

@@ -11684,11 +11684,22 @@ svg_load (struct frame *f, struct image *img)
   base_uri = image_spec_value (img->spec, QCbase_uri, NULL);
   if (STRINGP (file_name))
     {
+      image_fd fd;
+      Lisp_Object file = image_find_image_fd (file_name, &fd);
+      if (!STRINGP (file))
+	{
+	  image_not_found_error (file_name);
+	  return false;
+	}
+
+      /* Read the entire file into memory.  */
       ptrdiff_t size;
-      char *contents = slurp_image (file_name, &size, "SVG");
+      char *contents = slurp_file (fd, &size);
       if (contents == NULL)
-	return false;
-
+	{
+	  image_error ("Error loading SVG image `%s'", file);
+	  return false;
+	}
       /* If the file was slurped into memory properly, parse it.  */
       if (!STRINGP (base_uri))
         base_uri = file;