Fixes pipenet error supression (#64303)

Currently the pipenet system spams "build_pipeline(): further messages about pipenets will be suppressed" for every error after they've hit the supression threshold, which is worse than if it showed the actual info.

This PR knocks the countdown to -1 when the messages are suppressed so it never shows again, as intended. As a side note, why does nobody test their code for even the literally most common, intended use case?

Removes a pointless, useless source of log spam.

code/modules/atmospherics/machinery/datum_pipeline.dm

@@ -92,9 +92,9 @@
 					var/static/pipenetwarnings = 10
 					if(pipenetwarnings > 0)
 						log_mapping("build_pipeline(): [item.type] added to a pipenet while still having one. (pipes leading to the same spot stacking in one turf) around [AREACOORD(item)].")
-						pipenetwarnings--
 					if(pipenetwarnings == 0)
 						log_mapping("build_pipeline(): further messages about pipenets will be suppressed")
+					pipenetwarnings--
 
 				members += item
 				possible_expansions += item