Validate staticdata and object property length limits (#11511)

Some games provide users with enough freedom to create items
with metadata longer than 64KB, preventing this from causing
issues is on them but we'll still do the minimum not to abort
the server if this happens.

src/staticobject.cpp

@@ -37,6 +37,7 @@ void StaticObject::serialize(std::ostream &os)
 	// data
 	os<<serializeString16(data);
 }
+
 void StaticObject::deSerialize(std::istream &is, u8 version)
 {
 	// type
@@ -49,6 +50,29 @@ void StaticObject::deSerialize(std::istream &is, u8 version)
 
 void StaticObjectList::serialize(std::ostream &os)
 {
+	// Check for problems first
+	auto problematic = [] (StaticObject &obj) -> bool {
+		if (obj.data.size() > U16_MAX) {
+			errorstream << "StaticObjectList::serialize(): "
+				"object has excessive static data (" << obj.data.size() <<
+				"), deleting it." << std::endl;
+			return true;
+		}
+		return false;
+	};
+	for (auto it = m_stored.begin(); it != m_stored.end(); ) {
+		if (problematic(*it))
+			it = m_stored.erase(it);
+		else
+			it++;
+	}
+	for (auto it = m_active.begin(); it != m_active.end(); ) {
+		if (problematic(it->second))
+			it = m_active.erase(it);
+		else
+			it++;
+	}
+
 	// version
 	u8 version = 0;
 	writeU8(os, version);