oscplot.c: fix impulse generator

iio_device_get_trigger will return 0 on success, but if there is no device
assigned to the trigger, the trigger pointer will be NULL.
since the impulse generator menu sets the trigger, the condition will not
be satisfied. this resulted in the impulse generator menu being grayed out.
Now, we will only check that the return value is 0. The renaming of the
bool variable is to avoid confusion.

Signed-off-by: Cristina Suteu <[email protected]>

oscplot.c

@@ -6750,17 +6750,17 @@ static gboolean right_click_menu_show(OscPlot *plot, GdkEvent *event)
 		/* Check if device needs a trigger */
 		struct iio_device *dev = ref;
 		const struct iio_device *trigger;
-		bool has_trigger;
+		bool needs_trigger;
 		int ret;
 
 		ret = iio_device_get_trigger(dev, &trigger);
-		has_trigger = false;
-		if (ret == 0 && trigger) {
-			has_trigger = true;
+		needs_trigger = false;
+		if (ret == 0) {
+			needs_trigger = true;
 		}
 
 		gtk_widget_set_sensitive(priv->device_trigger_menuitem,
-				has_trigger);
+				needs_trigger);
 
 		gtk_menu_popup_at_pointer(GTK_MENU(priv->device_settings_menu), event);
 		return true;