gitweb.cgi: Create $git_temp if it doesn't exist

Unless we'd done diffs, $git_temp doesn't exist and then
mime lookups fail.  Explicitly create it, if it doesn't
exist already.

Signed-off-by: Luben Tuikov <ltuikov@yahoo.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

gitweb/gitweb.cgi

@@ -39,6 +39,9 @@ if ($git_version =~ m/git version (.*)$/) {
 
 # location for temporary files needed for diffs
 our $git_temp = "/tmp/gitweb";
+if (! -d $git_temp) {
+    mkdir($git_temp, 0700) || die_error("Couldn't mkdir $git_temp");
+}
 
 # target of the home link on top of all pages
 our $home_link = $my_uri;