Allocate RefMImage in the GC heap; fixes #1865 (#1934)

libs/core/images.cpp

@@ -40,7 +40,7 @@ namespace images {
 //% blockId=device_build_image block="create image"
 //% parts="ledmatrix"
 Image createImage(ImageLiteral_ leds) {
-    return new RefMImage(imageBytes(leds));
+    return NEW_GC(RefMImage, imageBytes(leds));
 }
 
 /**

libs/core/led.cpp

@@ -145,7 +145,7 @@ namespace led {
     //% parts="ledmatrix"
     Image screenshot() {
         auto d = uBit.display.screenShot().leakData();
-        auto r = new RefMImage(d);
+        auto r = NEW_GC(RefMImage, d);
         d->decr();
         return r;
         /*