Patch: Attempt to fix 2 compile warnings

[markdoliner]

The warnings are:

compress.c: In function '_sx_compress_wio':
compress.c:141: warning: 'return' with no value, in function returning non-void
compress.c: In function '_sx_compress_rio':
compress.c:202: warning: 'return' with no value, in function returning non-void

I'm not very familiar with this code, so please check to make sure my change is correct. The comment in sx.h says, "return -2 == failed (permanent), -1 == failed (temporary), 0 == handled, 1 == pass" It looks like the two functions are returning because compression is not enabled, in which case it seems like they should "pass" and the next function in the chain should attempt to read or write the data?

[smoku]

(In [439]) Fixes #167 function return values for compress rio/wio.