* mu4e-view: fill headers before display, so they don't run off the screen

emacs/mu4e-view.el

@@ -138,16 +138,17 @@ marking if it still had that."
 	(mu4e-view-mark-as-read-maybe)))))
 
   
-  
 (defun mu4e-view-header (key val &optional dont-propertize-val)
-  "Show header FIELD for MSG with KEY. ie. <KEY>: value-of-FIELD."
+  "Return header KEY with value VAL if VAL is non-nil. If
+DONT-PROPERTIZE-VAL, do not add text-properties to VAL."
   (if val
-    (concat
-      (propertize key 'face 'mu4e-view-header-key-face) ": "
+    (with-temp-buffer
+      (insert (propertize key 'face 'mu4e-view-header-key-face) ": "
 	(if dont-propertize-val
 	  val
-        (propertize val 'face 'mu4e-view-header-value-face))
-      "\n")
+	  (propertize val 'face 'mu4e-view-header-value-face)) "\n")
+      (fill-region (point-min) (point-max))
+      (buffer-string))
     ""))