MdeModulePkg: Fix conditionally uninitialized variables

Fixes CodeQL alerts for CWE-457:
https://cwe.mitre.org/data/definitions/457.html

Cc: Dandan Bi <dandan.bi@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Erich McMillan <emcmillan@microsoft.com>
Cc: Guomin Jiang <guomin.jiang@intel.com>
Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Michael Kubacki <mikuback@linux.microsoft.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Zhichao Gao <zhichao.gao@intel.com>
Co-authored-by: Erich McMillan <emcmillan@microsoft.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Oliver Smith-Denny <osd@smith-denny.com>

MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c

@@ -2453,7 +2453,7 @@ VariableServiceGetVariable (
   AcquireLockOnlyAtBootTime (&mVariableModuleGlobal->VariableGlobal.VariableServicesLock);
 
   Status = FindVariable (VariableName, VendorGuid, &Variable, &mVariableModuleGlobal->VariableGlobal, FALSE);
-  if ((Variable.CurrPtr == NULL) || EFI_ERROR (Status)) {
+  if (EFI_ERROR (Status) || (Variable.CurrPtr == NULL)) {
     goto Done;
   }