Make all nades do a regular explosion when they are destroyed

Make all nades do a regular explosion when they are destroyed

Previously nades would do nothing when they were destroyed (e.g. falling into lava, falling into void), except normal, napalm, and monster nade would explode (or only normal after cc7e64b6).
This commit makes them all do a normal nade explosion in such case.
This is better than doing nothing (nade would mysteriously disappear), or keeping the current sound & explosion effects (they would display, but the nade wouldn't actually do anything).