Fixes blood reagent runtimes

add_reagent was never creating blood with its default data, because it
always nulled out the data if none was provided

code/modules/reagents/Chemistry-Holder.dm

@@ -488,7 +488,7 @@ datum
 					R.holder = src
 					R.volume = amount
 //					SetViruses(R, data) // Includes setting data
-					R.data = data
+					if(data) R.data = data
 					//debug
 					//world << "Adding data"
 					//for(var/D in R.data)