BaseTools: Fix the build report crash issue

BaseTools: Fix the build report crash issue

In the following corner case, the build report
will crash. This patch is to fix this problem.

Case:
Multiple SKU are used and 2 more DynamicHii structure Pcds
are set in dsc file under different SKU. And 1 more of those
Pcds are not used in any INF file.

Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Yuwei Chen <yuwei.chen@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Yuwei Chen<yuwei.chen@intel.com>