Bug 1106843 -- msgfmt crashes when writing java source code and the .po file has a POT-Creation-Date header

Due d13f165b83701dffc14f7151419e0c00c00c0d1b there will be the
line with the POT-Creation-Date: tag removed but the lenght of
the changed message string does also change with this.

---
 gettext-tools/src/msgl-header.c |    1 +
 1 file changed, 1 insertion(+)

--- gettext-tools/src/msgl-header.c
+++ gettext-tools/src/msgl-header.c	2018-09-19 08:05:54.340122157 +0000
@@ -217,6 +217,7 @@ message_list_delete_header_field (messag
               *p = '\0';
 
             mp->msgstr = new_header;
+            mp->msgstr_len = strlen (new_header) + 1;
           }
       }
 }