BaseTools: Fix python error with --genfds-multi-thread.
BaseTools: Fix python error with --genfds-multi-thread.

When self.Alignment is None, it ran into python error since there is no
strip() in None.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Derek Lin <619c22d7be1ca1c616f219f81c899e30e55c21a8@hpe.com>
Reviewed-by: Yonghong Zhu <78d981fe33a016071af5222c56d5cf77f30fb0b2@intel.com>

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