fix(gui): guard gizmo actions before deferred initialization (#16268)

GLGizmosManager can be called while its gizmo list is empty, either at startup before the canvas has loaded the gizmos or after their init() failed. reset_all_states(), open_gizmo(), open_gizmo_by_shortcut() and activate_gizmo() now return early in that case. This fixes a Debug-build assert when a new project resets the gizmos at startup, and an out-of-bounds read in release builds when a gizmo shortcut key is pressed after gizmo init failed. activate_gizmo(Undefined) still returns true, since no gizmo is open. The reset_all_states() guard was first proposed in #16074 by kenrap.

Co-authored-by: kenrap <101818165+kenrap@users.noreply.github.com>

src/slic3r/GUI/Gizmos/GLGizmosManager.cpp

@@ -420,7 +420,10 @@ void GLGizmosManager::refresh_on_off_state()
 
 void GLGizmosManager::reset_all_states()
 {
-    if (! m_enabled || m_serializing)
+    // The restore/new-project event can run before deferred OpenGL resource
+    // loading has populated the gizmo list.  There is nothing to reset until
+    // initialization completes.
+    if (! m_enabled || m_serializing || m_gizmos.empty())
         return;
 
     const EType current = get_current_type();
@@ -435,6 +438,9 @@ void GLGizmosManager::reset_all_states()
 
 bool GLGizmosManager::open_gizmo(EType type)
 {
+    if (m_gizmos.empty())
+        return false;
+
     int idx = static_cast<int>(type);
 
     // re-open same type cause closing
@@ -522,7 +528,7 @@ bool GLGizmosManager::is_running() const
 
 bool GLGizmosManager::open_gizmo_by_shortcut(Shortcut shortcut)
 {
-    if (!m_enabled)
+    if (!m_enabled || m_gizmos.empty())
         return false;
 
     // The text tool opens without a selection because it creates its own object.
@@ -1427,10 +1433,12 @@ void GLGizmosManager::update_hover_state(const EType &type)
 
 bool GLGizmosManager::activate_gizmo(EType type)
 {
-    assert(!m_gizmos.empty());
-
     // already activated
-    if (m_current == type) return true;
+    if (m_current == type)
+        return true;
+
+    if (m_gizmos.empty())
+        return false;
 
     if (m_current != Undefined) {
         // clean up previous gizmo