Do not test debian changes, if file is not present.

Only run lintian if the changes file is present. This might not be the
case if for example a build.script is used that does not generate one
but still successfully completed, which should not cause lintian to
subsequently fail the build.

build-recipe-dsc

@@ -183,7 +183,9 @@ dsc_build() {
     chroot $buildroot su -c "export DEB_BUILD_OPTIONS='${DSC_BUILD_OPTIONS}' ; cd $TOPDIR/BUILD && $DSC_BUILD_CMD" - $BUILD_USER < /dev/null && BUILD_SUCCEEDED=true
     if test "$BUILD_SUCCEEDED" = true -a "$DO_CHECKS" != "false" && ( chroot $buildroot su -c "which lintian > /dev/null" - $BUILD_USER < /dev/null ); then
 	DEB_CHANGESFILE=${DEB_DSCFILE%.dsc}$OBS_DCH_RELEASE"_"$(chroot $buildroot su -c 'dpkg-architecture -qDEB_BUILD_ARCH')".changes"
-	chroot $buildroot su -c "cd $TOPDIR && echo Running lintian && (set -x && lintian -i $TOPDIR/$DEB_CHANGESFILE)" - $BUILD_USER < /dev/null || BUILD_SUCCEEDED=false
+	if test -e "$buildroot/$TOPDIR/$DEB_CHANGESFILE"; then
+	    chroot $buildroot su -c "cd $TOPDIR && echo Running lintian && (set -x && lintian -i $TOPDIR/$DEB_CHANGESFILE)" - $BUILD_USER < /dev/null || BUILD_SUCCEEDED=false
+	fi
     fi
 }