pipe led.plotbargraph through console.log (#1557)

libs/core/console.ts

@@ -46,7 +46,7 @@ namespace console {
     //%
     export function addListener(listener: (text: string) => void) {
         if (!listener) return;
-        if (!listener)
+        if (!listeners)
             listeners = [];
         listeners.push(listener);
     }

libs/core/led.ts

@@ -20,7 +20,7 @@
     //% parts="ledmatrix"
     export function plotBarGraph(value: number, high: number): void {
         const now = input.runningTime();
-        serial.writeLine(value.toString());
+        console.logValue("", value);
         value = Math.abs(value);
 
         // auto-scale "high" is not provided