Console: Reduce limit of concurrent graph generation on slow devices

apps/routerconsole/java/src/net/i2p/router/web/StatSummarizer.java

@@ -43,7 +43,7 @@ public class StatSummarizer implements Runnable, ClientApp {
     private final Log _log;
     /** list of SummaryListener instances */
     private final List<SummaryListener> _listeners;
-    private static final int MAX_CONCURRENT_PNG = SystemVersion.isARM() ? 2 : 3;
+    private static final int MAX_CONCURRENT_PNG = SystemVersion.isSlow() ? 1 : 3;
     private final Semaphore _sem;
     private volatile boolean _isRunning;
     private volatile Thread _thread;