Minor startup performance improvements (#2177)

changes:

Reduced Asteroid setup time by ~4 seconds on average.
Fixed a bug where jump-to-turf may have not worked on mine turfs.
Possible minor startup time improvements for SSair and Xenoarch.

code/modules/mining/mine_turfs.dm

@@ -47,6 +47,8 @@
 
 	initialized = TRUE
 
+	turfs += src
+
 	if(dynamic_lighting)
 		luminosity = 0
 	else
@@ -511,6 +513,8 @@
 		crash_with("Warning: [src]([type]) initialized multiple times!")
 	initialized = TRUE
 
+	turfs += src
+
 	if(dynamic_lighting)
 		luminosity = 0
 	else