Fix bug in scrolled single line wxTextCtrl::HitTest() with GTK 3

There seems to be something wrong with the vertical offset returned by
gtk_entry_get_layout_offsets() in GTK 3, so just don't use it at all, as
we don't need it anyhow.

src/gtk/textctrl.cpp

@@ -1451,7 +1451,17 @@ wxTextCtrl::HitTest(const wxPoint& pt, long *pos) const
         gtk_entry_get_layout_offsets(GTK_ENTRY(m_text), &ofsX, &ofsY);
 
         x -= ofsX;
+
+        // There is something really weird going on with vertical offset under
+        // GTK 3: normally it is just 0, because a single line control doesn't
+        // scroll vertically anyhow, but sometimes it can have big positive or
+        // negative values after scrolling horizontally, resulting in test
+        // failures in TextCtrlTestCase::HitTestSingleLine::Scrolled. So just
+        // ignore it completely, as, again, it shouldn't matter for single line
+        // text controls in any case, and so do not do this:
+#ifndef __WXGTK3__
         y -= ofsY;
+#endif // !__WXGTK3__
 
         // And scale the coordinates for Pango.
         x *= PANGO_SCALE;