Fix T77448: Camera Solver constraint can't be converted to f-curve

A regression caused by c57f65c088 as a fix of another issue.

Added an exception for camera solver as that is always pointing
to camera object.

Since this is a regression which happened in 2.83.0 this change is
a candidate to be ported to the 2.83.1.

release/scripts/startup/bl_operators/clip.py

@@ -486,7 +486,10 @@ class CLIP_OT_constraint_to_fcurve(Operator):
             return {'FINISHED'}
 
         # Find start and end frames.
-        if con.object:
+        if con.type == 'CAMERA_SOLVER':
+            # Camera solver constraint is always referring to camera.
+            tracks = clip.tracking.tracks
+        elif con.object:
             tracking_object = clip.tracking.objects.get(con.object, None)
             if not tracking_object:
                 self.report({'ERROR'}, "Motion Tracking object not found")