Fix: Crash with single point bezier spline auto handles

There's no way to calculate auto or vector handles when there is
only one point, and returning early allows avoiding checking for
that case later on.

source/blender/blenkernel/intern/spline_bezier.cc

@@ -214,6 +214,11 @@ void BezierSpline::ensure_auto_handles() const
     return;
   }
 
+  if (this->size() == 1) {
+    auto_handles_dirty_ = false;
+    return;
+  }
+
   for (const int i : IndexRange(this->size())) {
     if (ELEM(HandleType::Auto, handle_types_left_[i], handle_types_right_[i])) {
       const float3 prev_diff = positions_[i] - previous_position(positions_, is_cyclic_, i);