BaseTools: Fix a bug for single module build with GenC/GenMake option

BaseTools: Fix a bug for single module build with GenC/GenMake option

when build a single module with GenC/GenMake option, currently it will
direct return after create Autogen code files, then it cause MaList is
empty, which cause an incorrect error message is reported.

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