Fix: Crash when trying to get FCurve segments of baked curve

When using the slider operators in the Graph Editor
the code would try to access `FCurve.bezt` without checking that exists.
When the curve is baked that is a null pointer.

Pull Request: https://projects.blender.org/blender/blender/pulls/106102

source/blender/editors/animation/keyframes_general.c

@@ -279,6 +279,12 @@ static bool find_fcurve_segment(FCurve *fcu,
 ListBase find_fcurve_segments(FCurve *fcu)
 {
   ListBase segments = {NULL, NULL};
+
+  /* Ignore baked curves. */
+  if (!fcu->bezt) {
+    return segments;
+  }
+
   int segment_start_idx = 0;
   int segment_len = 0;
   int current_index = 0;