particle/progress-bar: fix ‘where’ tag regression

After implementing support for more mouse buttons (and scrolling), the
‘where’ tag stopped working in the progress-bar.

This patch repairs it.

CHANGELOG.md

@@ -26,6 +26,8 @@
 
 * `yambar --backend=wayland` always erroring out with _”yambar was
   compiled without the Wayland backend”_.
+* Regression: `{where}` tag not being expanded in progress-bar
+  `on-click` handlers.
 
 
 ### Security