[mobile-broadband-provider-info] build: add an indentation check

[Lubomir Rintel <lkundrak src gnome org>]

commit f062554934b5e9d330d36c4a90611ac52e476ff0
Author: Lubomir Rintel <lkundrak v3 sk>
Date:   Wed Mar 16 16:14:20 2022 +0100

    build: add an indentation check

 Makefile.am | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index 52aa99c..a92c5be 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -18,5 +18,5 @@ apns-conf.xml: $(top_srcdir)/apns-conf.xsl $(top_srcdir)/$(SP_XML_DB)
 pkgdata_DATA = apns-conf.xml
 
 check-local:
-       xmllint --valid $(top_srcdir)/$(SP_XML_DB) 2>&1 > /dev/null || exit 1;
-
+       grep '^[\t ]* <' serviceproviders.xml && exit 1 || :
+       xmllint --valid $(top_srcdir)/$(SP_XML_DB) 2>&1 >/dev/null