cgit.c: always setup cgit repo environment variables

When cgit learned to setup environment variables for certain repo
settings before invoking a filter process, the setup occurred inside
cgit_open_filter().

This patch moves the setup out of cgit_open_filter() and into
prepare_repo_cmd() to prepare for additional uses of these variables.

Reviewed-by: Ferry Huberts <mailings@hupie.com>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.c

@@ -463,6 +463,7 @@ static int prepare_repo_cmd(struct cgit_context *ctx)
 		cgit_print_docend();
 		return 1;
 	}
+	cgit_prepare_repo_env(ctx->repo);
 	return 0;
 }