Makefile: install html files in install-txt

The project git-html-l10n awaits html files.

Signed-off-by: Jean-Noël Avila <jn.avila@free.fr>

makefile.locale

@@ -62,7 +62,8 @@ all doc-l10n: man html
 
 install-txt:
 	install -d -m 755 $(prefix)/$(lang)
-	install *.txt -m 644 $(prefix)/$(lang)
+	[ -z "$$(ls *.txt 2>/dev/null)" ] || install *.txt -m 644 $(prefix)/$(lang)
+	[ -z "$$(ls *.html 2>/dev/null)" ] || install *.html -m 644 $(prefix)/$(lang)
 
 clean:
 	rm -f *.1 *.html