Merge branch 'master' into jgrpp

# Conflicts:
#	CMakeLists.txt
#	src/bootstrap_gui.cpp

src/saveload/oldloader_sl.cpp

@@ -446,7 +446,7 @@ static bool FixTTOEngines()
 		e->preview_company = INVALID_COMPANY;
 		e->preview_asked = (CompanyMask)-1;
 		e->preview_wait = 0;
-		e->name = nullptr;
+		e->name = std::string{};
 	}
 
 	return true;

src/saveload/saveload.cpp

@@ -1941,7 +1941,7 @@ void SlObject(void *object, const SaveLoad *sld)
 	}
 
 	for (; sld->cmd != SL_END; sld++) {
-		void *ptr = sld->global ? sld->address : GetVariableAddress(object, sld);
+		void *ptr = GetVariableAddress(object, sld);
 		SlObjectMember(ptr, sld);
 	}
 }

src/saveload/saveload.h

@@ -1038,7 +1038,18 @@ static inline bool IsNumericType(VarType conv)
  */
 static inline void *GetVariableAddress(const void *object, const SaveLoad *sld)
 {
-	return const_cast<byte *>((const byte*)(sld->global ? nullptr : object) + (ptrdiff_t)sld->address);
+	/* Entry is a global address. */
+	if (sld->global) return sld->address;
+
+	/* Entry is a null-variable, mostly used to read old savegames etc. */
+	if (GetVarMemType(sld->conv) == SLE_VAR_NULL) {
+		assert(sld->address == nullptr);
+		return nullptr;
+	}
+
+	/* Everything else should be a non-null pointer. */
+	assert(object != nullptr);
+	return const_cast<byte *>((const byte *)object + (ptrdiff_t)sld->address);
 }
 
 int64 ReadValue(const void *ptr, VarType conv);