Plant Analyzer chemical tab bluescreen fix on starthistle seeds (#96669)

## About The Pull Request

When scanning the chemical contents of the starthistle seeds and corpse
flowers, the plant analyzer TGUI menu threw a bluescreen related to a
null list. This PR fixes that.

The actual problem was that in
`code/game/objects/items/devices/scanners/plant_analyzer.dm:285`,
`make_seed_data` proc which was responsible for collecting seed data to
send to the TGUI only ever initialized the `distill_reagent`,
`juice_name` and `grind_results` list entries when the plant had a
produce - which starthistles and corpse flowers do not have. I fixed it
by simply initializing these 2 entries as empty at the beginning of the
proc.

## Why It's Good For The Game

Fixes a UI bluescreen.

Before:
<img width="851" height="708" alt="image"
src="https://github.com/user-attachments/assets/16870d25-ece2-4d66-afca-53bd598a63ec"
/>
Upon opening the chemical tab of the plant analyzer when analyzing
corpse flowers, the tab bluescreens.

After:
<img width="896" height="807" alt="image"
src="https://github.com/user-attachments/assets/ff74e799-edef-4c10-97d9-42d4b650338d"
/>
The chemical tab not bluescreening.

code/game/objects/items/devices/scanners/plant_analyzer.dm

@@ -303,6 +303,9 @@
 	)
 	seed_data["removable_traits"] = list()
 	seed_data["core_traits"] = list()
+	seed_data["distill_reagent"] = ""
+	seed_data["juice_name"] = ""
+	seed_data["grind_results"] = list()
 	for(var/datum/plant_gene/trait/trait in seed.genes)
 		if(trait.mutability_flags & PLANT_GENE_REMOVABLE)
 			seed_data["removable_traits"] += trait.type