BUG #11991: dangerous action of pg_dump

The following bug has been logged on the website:

Bug reference:      11991
Logged by:          Tomasz Kimaczynski
Email address:      tomek@rai.pl
PostgreSQL version: 9.2.9
Operating system:   Windows 2003,2008,2012 & FreeBSD
Description:

Recently, I realized pg_dump dangerous activity. In case when no dump is
made because of any error, created file size is 0 bytes. In case when this
file is used in simple backup procedure which make copy of dump file - 0
bytes files overwrite earlier correct dump files.
And we have no copies.
Conclusion: pg_dump can not create 0 bytes files - it should create
nothing.
I think it's important.