Support Walk / Fly navigation if constraints are turned off

Currently, if you have constraint on your active camera and try to navigate from it in Walk/Fly mode using Shift + ² (or Shift + ` depending on your keyboard layout), an error message appears saying "Cannot navigate an object with constraints" , even if all the constraints are turned off.

However, you can navigate and transform it using other means, such as enabling the "Camera to View" Lock and using the MMB to orbit, pan and zoom, or using G, S, and R to grab, scale and rotate it. Even if the contraints are turned on, the transform values update based on your mouse movement, while the viewport shows the constrained result.

Maybe the Walk/Fly navigation is disabled for a good reason (loss of control) but if all the constraints are turned off, I see no reason not to support it.

This would be useful to me, as I use my camera to look around when editing my scene but need to constrain it whenever I hit Render. I can't repeatedly delete and put my constraints back, so right now I use a copy of my camera without the constraints, at the risk of accidentally rendering with it.

You might say "but if your request was granted and you used a single camera, then you'd be at risk of hitting render before re-enabling the constraints" , and you'd be right, but :

1. I'm sure at some point constraints will have 2 on/off buttons, one for the Viewport and one for the Render, just like modifiers (might be the subject of another feature request)
2. This is only one potential use case I described. There may be others.