BaseTools: Fix parsing multiple nest !include issue

BaseTools: Fix parsing multiple nest !include issue

Fix the bug !include file in Components subsection meet syntax error.

Case example:
DSC components:
!include Test1.txt

Test1.txt:
 TestPkg/TestDriver.inf {
   <PcdsFixedAtBuild>
    PcdToken.PcdTest1 | "A"
    !include Test2.txt
  }

Test2.txt:
!include Test3.txt

Test3.txt:
PcdToken.PcdTest2 | "B"

Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Yunhua Feng <yunhuax.feng@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>