ob-core.el (org-babel-load-in-session): Throw a useful error when there is no code block at point

* ob-core.el (org-babel-load-in-session): Throw a useful error
when there is no code block at point.

lisp/ob-core.el

@@ -758,10 +758,12 @@ session."
   (let* ((info (or info (org-babel-get-src-block-info)))
          (lang (nth 0 info))
          (params (nth 2 info))
-         (body (setf (nth 1 info)
-		     (if (org-babel-noweb-p params :eval)
-                         (org-babel-expand-noweb-references info)
-		       (nth 1 info))))
+         (body (if (not info)
+		   (user-error "No src code block at point")
+		 (setf (nth 1 info)
+		       (if (org-babel-noweb-p params :eval)
+			   (org-babel-expand-noweb-references info)
+			 (nth 1 info)))))
          (session (cdr (assoc :session params)))
 	 (dir (cdr (assoc :dir params)))
 	 (default-directory