Fix some errors and warnings when compiling with Clang

Sources/Plasma/CoreLib/hsRefCnt.h

@@ -43,6 +43,7 @@ You can contact Cyan Worlds, Inc. by email legal@cyan.com
 #define hsRefCnt_Defiend
 
 #include <atomic>
+#include <cstddef>
 
 class hsRefCnt {
 private:
@@ -83,7 +84,7 @@ class hsRef
 {
 public:
     hsRef() : fObj(nullptr) { }
-    hsRef(nullptr_t) : fObj(nullptr) { }
+    hsRef(std::nullptr_t) : fObj(nullptr) { }
     hsRef(_Ref *obj) : fObj(obj) { if (fObj) fObj->Ref(); }
     hsRef(const hsRef<_Ref> &copy) : fObj(copy.fObj) { if (fObj) fObj->Ref(); }
     hsRef(hsRef<_Ref> &&move) : fObj(move.fObj) { move.fObj = nullptr; }
@@ -110,7 +111,7 @@ public:
         return *this;
     }
 
-    hsRef<_Ref> &operator=(nullptr_t)
+    hsRef<_Ref> &operator=(std::nullptr_t)
     {
         if (fObj)
             fObj->UnRef();

Sources/Plasma/FeatureLib/pfGameGUIMgr/pfGUIListElement.h

@@ -226,6 +226,7 @@ class pfGUIDropTargetProc
     public:
 
         pfGUIDropTargetProc() { fRefCnt = 0; }
+        virtual ~pfGUIDropTargetProc() { }
 
         virtual bool    CanEat( pfGUIListElement *element, pfGUIControlMod *source ) = 0;
         virtual void    Eat( pfGUIListElement *element, pfGUIControlMod *source, pfGUIControlMod *parent ) = 0;

Sources/Plasma/NucleusLib/pnUtils/pnUtCrypt.cpp

@@ -154,7 +154,7 @@ void CryptKeyClose (
     if (!key)
         return;
 
-    delete key->handle;
+    delete (RC4_KEY *)key->handle;
     delete key;
 }