TestBench: Small fix

Check if the "on" signal ends with "Changed" to make
sure we are dealing with a property.

I.e. onClicked should be skipped. Also in that case
it caused the substr to be empty and the call
item[substr] to create an assert in V8.

Change-Id: Ib04aa1773ef13a005e998659c7c903d3118bfc62
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>

tests/manual/testbench/main.qml

@@ -123,7 +123,10 @@ ApplicationWindow {
                         propertyModel.clear()
 
                         for (var prop in item) {
+
                             if (!prop.indexOf("on")) { // look only for properties
+                                if (prop.indexOf("Changed") !== (prop.length - 7))
+                                    continue
                                 var substr = prop.slice(2, prop.length - 7)
                                 if (!substr.indexOf("__")) // filter private
                                     continue;