Fix new summary-line after editing an article in Gnus

* lisp/gnus/gnus-sum.el (gnus-summary-edit-article-done): Strip ^M
from the ends of lines after saving an edited article. Otherwise the
new header isn't always parsed properly, resulting in an incorrect
subject line in the summary buffer.

lisp/gnus/gnus-sum.el

@@ -10708,6 +10708,7 @@ groups."
 	    ;; We only have to update this line.
 	    (save-excursion
 	      (save-restriction
+		(nnheader-ms-strip-cr)
 		(message-narrow-to-head)
 		(let ((head (buffer-substring-no-properties
 			     (point-min) (point-max)))