vcs-svn: simplify cleanup in apply_one_window

vcs-svn: simplify cleanup in apply_one_window

Currently the cleanup code looks like this:

	free resources
	return 0;
 error_out:
	free resources
	return -1;

Avoid duplicating the "free resources" part by keeping the return
value in a variable and sharing code between the success and
exceptional case:

	ret = 0;
 out:
	free resources
	return ret;

Noticed in the svn-dump-fast-export project, where using the error()
macro in void context produces a warning.

Signed-off-by: David Barr <davidbarr@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>