BaseTools: enhance error handling for DSC file

Add logic for DSC file validation for Prebuild init. Add logic to detect
error for DSC parser when '{' is missing.

Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

BaseTools/Source/Python/Workspace/MetaFileParser.py

@@ -915,6 +915,8 @@ class DscParser(MetaFileParser):
             elif Line[0] == '!':
                 self._DirectiveParser()
                 continue
+            if Line[0] == TAB_OPTION_START and not self._InSubsection:
+                EdkLogger.error("Parser", FILE_READ_FAILURE, "Missing the '{' before %s in Line %s" % (Line, Index+1),ExtraData=self.MetaFile)
 
             if self._InSubsection:
                 SectionType = self._SubsectionType