Steps To Reproduce:

1. Create a new Project
2. Hierarchy > Light > Reflection Probe
3. Select Reflection Probe in hierarchy to view in the inspector
4. Change the Type to Custom
5. Click on the select button of cubemap texture and select the texture that appears by default

Expected Result: An error or preferrably a warning, clearly stating that a 2D texture could not be assigned to the reflection probe cubemap is shown. The errors or warnings are not shown in an neverending loop.

Observed Result: Errors is intfinitely thrown in the console

Stack Trace: Error assigning 2D texture to CUBE texture property '_MainTex': Dimensions must match
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)

Reproducible On: 2019.3.0a3, 2019.2.0b3

Not Reproducible On: 2019.2.0b2

Environment: Win and Mac