Don't corrupt stepheight when setting other properties

src/script/common/c_content.cpp

@@ -191,8 +191,8 @@ void read_object_properties(lua_State *L, int index,
 	getboolfield(L, -1, "is_visible", prop->is_visible);
 	getboolfield(L, -1, "makes_footstep_sound", prop->makes_footstep_sound);
 	getfloatfield(L, -1, "automatic_rotate", prop->automatic_rotate);
-	getfloatfield(L, -1, "stepheight", prop->stepheight);
-	prop->stepheight*=BS;
+	if (getfloatfield(L, -1, "stepheight", prop->stepheight))
+		prop->stepheight *= BS;
 	lua_getfield(L, -1, "automatic_face_movement_dir");
 	if (lua_isnumber(L, -1)) {
 		prop->automatic_face_movement_dir = true;