ccj: fix mouse wheel input in overlay (#754)

## Link to GitHub Issue or related Pull Request, if one exists
#251 

## Description of change
CCJ registers for rawinput mouse. We allowed the rawinput registration
to go through to the OS, which prevents spice's rawinput stack from
using the mouse. This caused the overlay to not accept mouse input. Fix
it by not letting the rawinput registration through. Luckily, mouse
input continues to work properly in CCJ (for touch).

Also, fix a bug in DX11 overlay when toggling the main menu.

## Testing

src/spice2x/overlay/overlay.cpp

@@ -844,7 +844,10 @@ void overlay::SpiceOverlay::show_main_menu() {
         }
         return;
     }
-    if (ImGui::IsPopupOpen(0, ImGuiPopupFlags_AnyPopup)) {
+
+    // don't open on top of another genuinely-visible popup, but ONLY guard while
+    // the overlay is active
+    if (this->get_active() && ImGui::IsPopupOpen(0, ImGuiPopupFlags_AnyPopup)) {
         return;
     }