When a bitmap is empty bitmap_scnlistprintf() would leave the buffer
uninitialized.  Set it to an empty string in this case.

I didn't see any in normal kernel callers hitting this, but some custom
debug code of mine did.
Signed-off-by: NAndi Kleen <ak@suse.de>
Acked-by: NPaul Jackson <pj@sgi.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>