Makes the asset cache faster (#35003)

Winexists contacts the client and blocks, slowing down asset cache sends needlessly.

We now send multiple assets between verified sends. speeding up how quick preloading happen and reducing the number of junk files created in the clients cache.

code/modules/client/asset_cache.dm

@@ -17,6 +17,9 @@ You can set verify to TRUE if you want send() to sleep until the client has the
 //When sending mutiple assets, how many before we give the client a quaint little sending resources message
 #define ASSET_CACHE_TELL_CLIENT_AMOUNT 8
 
+//When passively preloading assets, how many to send at once? Too high creates noticable lag where as too low can flood the client's cache with "verify" files
+#define ASSET_CACHE_PRELOAD_CONCURRENT 3
+
 /client
 	var/list/cache = list() // List of all assets sent to this client by the asset cache.
 	var/list/completed_asset_jobs = list() // List of all completed jobs, awaiting acknowledgement.
@@ -42,12 +45,9 @@ You can set verify to TRUE if you want send() to sleep until the client has the
 		return 0
 
 	client << browse_rsc(SSassets.cache[asset_name], asset_name)
-	if(!verify || !winexists(client, "asset_cache_browser")) // Can't access the asset cache browser, rip.
-		if (client)
-			client.cache += asset_name
+	if(!verify)
+		client.cache += asset_name
 		return 1
-	if (!client)
-		return 0
 
 	client.sending |= asset_name
 	var/job = ++client.last_asset_job
@@ -94,12 +94,10 @@ You can set verify to TRUE if you want send() to sleep until the client has the
 		if (asset in SSassets.cache)
 			client << browse_rsc(SSassets.cache[asset], asset)
 
-	if(!verify || !winexists(client, "asset_cache_browser")) // Can't access the asset cache browser, rip.
-		if (client)
-			client.cache += unreceived
+	if(!verify) // Can't access the asset cache browser, rip.
+		client.cache += unreceived
 		return 1
-	if (!client)
-		return 0
+		
 	client.sending |= unreceived
 	var/job = ++client.last_asset_job
 
@@ -125,12 +123,19 @@ You can set verify to TRUE if you want send() to sleep until the client has the
 //This proc will download the files without clogging up the browse() queue, used for passively sending files on connection start.
 //The proc calls procs that sleep for long times.
 /proc/getFilesSlow(var/client/client, var/list/files, var/register_asset = TRUE)
+	var/concurrent_tracker = 1
 	for(var/file in files)
 		if (!client)
 			break
 		if (register_asset)
-			register_asset(file,files[file])
-		send_asset(client,file)
+			register_asset(file, files[file])
+		if (concurrent_tracker >= ASSET_CACHE_PRELOAD_CONCURRENT)
+			concurrent_tracker = 1
+			send_asset(client, file)
+		else
+			concurrent_tracker++
+			send_asset(client, file, verify=FALSE)
+			
 		stoplag(0) //queuing calls like this too quickly can cause issues in some client versions
 
 //This proc "registers" an asset, it adds it to the cache for further use, you cannot touch it from this point on or you'll fuck things up.