gitweb: die when a configuration file cannot be read

Fix a possibility of a permission to access error go unnoticed.

Perl uses two different variables to manage errors from a "do
$filename" construct. One is $@, which is set in this case when do
is unable to compile the file. The other is $!, which is set in case
do cannot read the file.  The current code only checks "$@", which
means a configuration file passed to GitWeb that is not readable by
the server process does not cause it to "die".

Make sure we also check and act on "$!" to fix this.

Signed-off-by: Marcelo Roberto Jimenez <marcelo.jimenez@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -728,9 +728,11 @@ sub filter_and_validate_refs {
 sub read_config_file {
 	my $filename = shift;
 	return unless defined $filename;
-	# die if there are errors parsing config file
 	if (-e $filename) {
 		do $filename;
+		# die if there is a problem accessing the file
+		die $! if $!;
+		# die if there are errors parsing config file
 		die $@ if $@;
 		return 1;
 	}