MdeModulePkg/SMM: Initialize 'WillReturn' variable

The local variable 'WillReturn' was being used without prior
initialization in some code paths.
This patch ensures that 'WillReturn' is properly initialized
to prevent undefined behavior.

Signed-off-by: Zhiguang Liu <zhiguang.liu@intel.com>

MdeModulePkg/Core/PiSmmCore/Smi.c

@@ -152,6 +152,7 @@ SmiManage (
 
   PERF_FUNCTION_BEGIN ();
   mSmiManageCallingDepth++;
+  WillReturn   = FALSE;
   Status       = EFI_NOT_FOUND;
   ReturnStatus = Status;
   if (HandlerType == NULL) {