gitweb: fix unmatched div in commitdiff

When the last filepair changed only metainfo we failed to close the
extended header <div>.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

gitweb/gitweb.perl

@@ -2338,6 +2338,8 @@ sub git_patchset_body {
 
 		print format_diff_line($patch_line);
 	}
+	print "</div>\n" if $in_header; # extended header
+
 	print "</div>\n" if $patch_found; # class="patch"
 
 	print "</div>\n"; # class="patchset"