po2msg: ignore untranslated messages

Do not generate translations when the translated message is empty.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

po/po2msg.sh

@@ -62,6 +62,9 @@ proc flush_msg {} {
 	if {$msgid == ""} {
 		set prefix "set ::msgcat::header"
 	} else {
+		if {$msgstr == ""} {
+			return
+		}
 		set prefix "::msgcat::mcset $lang \"[u2a $msgid]\""
 	}