PcAtChipsetPkg/PcRtc: Handle NULL table entry in RSDT/XSDT

The ACPI code may reserve the first entry for a certain table
(might be FACS) to help with OS compatible issues.
We need to skip the NULL table entry in RSDT/XSDT.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>

PcAtChipsetPkg/PcatRealTimeClockRuntimeDxe/PcRtc.c

@@ -1230,6 +1230,11 @@ ScanTableInSDT (
     //
     Table = 0;
     CopyMem (&Table, (VOID *) (EntryBase + Index * TablePointerSize), TablePointerSize);
+
+    if (Table == NULL) {
+      continue;
+    }
+
     if (Table->Signature == Signature) {
       return Table;
     }