C4Set: Replace elements with zero-initialized ones on clear

C4Set used to set its removed elements to nullptr. This requires
some special handling from non-pointer entries like C4Property.
Overwriting the element with a zero-initialized one removes this
requirement, leading to improved type safety on the part of
C4Property.

src/script/C4PropList.h

@@ -54,8 +54,6 @@ class C4Property
 	C4String * Key{nullptr};
 	C4Value Value;
 	operator const void * () const { return Key; }
-	C4Property & operator = (void * p)
-	{ assert(!p); if (Key) Key->DecRef(); Key = nullptr; Value.Set0(); return *this; }
 	bool operator < (const C4Property &cmp) const { return strcmp(GetSafeKey(), cmp.GetSafeKey())<0; }
 	const char *GetSafeKey() const { if (Key && Key->GetCStr()) return Key->GetCStr(); return ""; } // get key as C string; return "" if undefined. never return nullptr
 };

src/script/C4StringTable.h

@@ -2,7 +2,7 @@
  * OpenClonk, http://www.openclonk.org
  *
  * Copyright (c) 2001-2009, RedWolf Design GmbH, http://www.clonk.de/
- * Copyright (c) 2009-2016, The OpenClonk Team and contributors
+ * Copyright (c) 2009-2019, The OpenClonk Team and contributors
  *
  * Distributed under the terms of the ISC license; see accompanying file
  * "COPYING" for details.
@@ -145,7 +145,7 @@ template<typename T> class C4Set
 	void ClearTable()
 	{
 		for (unsigned int i = 0; i < Capacity; ++i)
-			Table[i] = nullptr;
+			Table[i] = T{};
 	}
 	void MaintainCapacity()
 	{
@@ -240,13 +240,13 @@ template<typename T> class C4Set
 			r = &Table[++h % Capacity];
 		}
 		assert(*r);
-		*r = nullptr;
+		*r = T{};
 		--Size;
 		// Move entries which might have collided with e
 		while (*(r = &Table[++h % Capacity]))
 		{
 			T m = *r;
-			*r = nullptr;
+			*r = T{};
 			AddInternal(std::move(m));
 		}
 	}