gitweb: Check if requested object exists

Try to avoid "Use of uninitialized value ..." errors caused by bad
revision, incorrect filename, wrong object id, bad file etc. (wrong
value of 'h', 'hb', 'f', etc. parameters). This avoids polluting web
server errors log.

Correct git_get_hash_by_path and parse_commit_text (and, in turn,
parse_commit) to return undef if object does not exist.  Check in
git_tag if requested tag exists.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

gitweb/gitweb.perl

@@ -1060,6 +1060,11 @@ sub git_get_hash_by_path {
 	my $line = <$fd>;
 	close $fd or return undef;
 
+	if (!defined $line) {
+		# there is no tree or hash given by $path at $base
+		return undef;
+	}
+
 	#'100644 blob 0fa3f3a66fb6a137f6ec2c19351ed4d807070ffa	panic.c'
 	$line =~ m/^([0-9]+) (.+) ([0-9a-fA-F]{40})\t/;
 	if (defined $type && $type ne $2) {
@@ -1376,8 +1381,12 @@ sub parse_commit_text {
 
 	pop @commit_lines; # Remove '\0'
 
+	if (! @commit_lines) {
+		return;
+	}
+
 	my $header = shift @commit_lines;
-	if (!($header =~ m/^[0-9a-fA-F]{40}/)) {
+	if ($header !~ m/^[0-9a-fA-F]{40}/) {
 		return;
 	}
 	($co{'id'}, my @parents) = split ' ', $header;
@@ -3409,6 +3418,11 @@ sub git_tag {
 	git_header_html();
 	git_print_page_nav('','', $head,undef,$head);
 	my %tag = parse_tag($hash);
+
+	if (! %tag) {
+		die_error(undef, "Unknown tag object");
+	}
+
 	git_print_header_div('commit', esc_html($tag{'name'}), $hash);
 	print "<div class=\"title_text\">\n" .
 	      "<table cellspacing=\"0\">\n" .