OpenDream Compile Fixes (#22518)

Fixes a handful of errors that prevented this codebase from compiling
with OpenDream. I have tested this.

<img width="1915" height="988" alt="image"
src="https://github.com/user-attachments/assets/6f04fa2b-1d08-484d-9fe4-2a3ff7d95a18"
/>

code/__DEFINES/rust_g.dm

@@ -33,7 +33,7 @@
 			// It's not in the current directory, so try others
 			return __rust_g = "librust_g.so"
 	else
-		return __rust_g = "rust_g"
+		return __rust_g = "rust_g.dll"
 
 #define RUST_G (__rust_g || __detect_rust_g())
 #endif

code/game/dna/genes/disabilities.dm

@@ -10,19 +10,19 @@
 	name="DISABILITY"
 
 	// Mutation to give (or 0)
-	var/mutation=0
+	var/mutation
 
 	// Disability to give (or 0)
-	var/disability=0
+	var/disability
 
 	// SDisability to give (or 0)
-	var/sdisability=0
+	var/sdisability
 
 	// Activation message
-	var/activation_message=""
+	var/activation_message
 
 	// Yay, you're no longer growing 3 arms
-	var/deactivation_message=""
+	var/deactivation_message
 
 /datum/dna/gene/disability/can_activate(var/mob/M,var/flags)
 	return 1 // Always set!