bionic: fix NULL parameter failure in getcwd()

LTP: getcwd01 failed in LTP

Need to check getcwd parameters, otherwise it will lead to
posix test case to fail.

Change-Id: Ieb673b6dd4ca6481da81c5339dbf7ec0a463f263
Signed-off-by: Jin Wei <wei.a.jin@intel.com>
Signed-off-by: Jack Ren <jack.ren@intel.com>
Signed-off-by: Bruce Beare <bruce.j.beare@intel.com>