BaseTools: Fix UEFI and Tiano Decompression logic issue

BaseTools: Fix UEFI and Tiano Decompression logic issue

https://bugzilla.tianocore.org/show_bug.cgi?id=1317

This is a regression issue caused by 041d89bc0f0119df37a5fce1d0f16495ff905089.
In Decode() function, once mOutBuf is fully filled, Decode() should return.
Current logic misses the checker of mOutBuf after while() loop.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>