Add nullptr check for kv delete operator

tier1/KeyValues.cpp

@@ -2806,12 +2806,18 @@ void *KeyValues::operator new( size_t iAllocSize, int nBlockUse, const char *pFi
 //-----------------------------------------------------------------------------
 void KeyValues::operator delete( void *pMem )
 {
-	KeyValuesSystem()->FreeKeyValuesMemory(pMem);
+	if (pMem)
+	{
+		KeyValuesSystem()->FreeKeyValuesMemory(pMem);
+	}
 }
 
 void KeyValues::operator delete( void *pMem, int nBlockUse, const char *pFileName, int nLine )
 {
-	KeyValuesSystem()->FreeKeyValuesMemory(pMem);
+	if (pMem)
+	{
+		KeyValuesSystem()->FreeKeyValuesMemory(pMem);
+	}
 }
 
 void KeyValues::UnpackIntoStructure( KeyValuesUnpackStructure const *pUnpackTable, void *pDest, size_t DestSizeInBytes )