Fix the issue that might prevent single step in PeCoffExtraActionLib (right after triggering breakpoint to notify image load/unload) work.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@10870 6f19259b-4bc3-4df7-8a09-765794883524

SourceLevelDebugPkg/Library/DebugAgent/DebugAgentCommon/DebugAgent.c

@@ -384,6 +384,11 @@ GetBreakCause (
       //
       if ((CpuContext->Dr6 & BIT14) != 0) {
         Cause = DEBUG_DATA_BREAK_CAUSE_STEPPING;
+        //
+        // If it's single step, no need to check DR0, to ensure single step work in PeCoffExtraActionLib
+        // (right after triggering a breakpoint to report image load/unload).
+        //
+        return Cause;
 
       } else {
         Cause = DEBUG_DATA_BREAK_CAUSE_HW_BREAKPOINT;