Fixes stacking explosions in overloaded escape pods (#7080)

# About the pull request

Fixes #7071

This moves the SHUTTLE_CRASHED assignment in prepare_evac() to before
the sleeps during the escape pod overload sequence, preventing a user
from queueing up several launches before the explosion is triggered. As
a side effect, this also displays an error on the launch screen after
you attempt to launch it.

Although this issue is quite funny, being able to one-shot nearly any
xeno using an escape pod definitely isn't intentional.
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# Explain why it's good for the game
Bugfix.


# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>


https://github.com/user-attachments/assets/2c345e96-d847-4248-bf29-7190767fd80b




</details>


# Changelog
:cl:
fix: Fixes stacking explosions in overloaded escape pods.
/:cl:

code/modules/shuttle/shuttles/crashable/escape_shuttle.dm

@@ -78,11 +78,11 @@
 			cryos += list(cryotube)
 	if (occupant_count > max_capacity)
 		playsound(src,'sound/effects/escape_pod_warmup.ogg', 50, 1)
+		mode = SHUTTLE_CRASHED
 		sleep(31)
 		var/turf/sploded = return_center_turf()
 		cell_explosion(sploded, 100, 20, EXPLOSION_FALLOFF_SHAPE_LINEAR, null, create_cause_data("escape pod malfunction")) //Clears out walls
 		sleep(25)
-		mode = SHUTTLE_CRASHED
 		for(var/obj/structure/machinery/cryopod/evacuation/cryotube in cryos)
 			cryotube.go_out()
 		door_handler.control_doors("force-unlock")