How to reproduce:
1. Open the attached project named "Case_1326754"
2. Open the "DemoScene1"
3. Observe the Console window. If no error message is thrown, enter Play mode

Expected results: No errors are thrown and the text is correctly displayed in Scene and Game windows
Actual results: NullReferenceException is thrown and the text is not rendered

Reproducible with: 1.4.1(2018.4.35f1), 2.1.6(2019.4.26f1), 3.0.6(2020.3.8f1, 2021.1.7f1, 2021.2.0a17)

Notes:
1. The error in the test project seems to be caused by a <font> and <sprite name="Smiling face with smiling eyes"> tags combination

Full error message:
NullReferenceException: Object reference not set to an instance of an object
TMPro.TextMeshProUGUI.GenerateTextMesh () (at Library/PackageCache/com.unity.textmeshpro@3.0.6/Scripts/Runtime/TMPro_UGUI_Private.cs:2024)
TMPro.TextMeshProUGUI.OnPreRenderCanvas () (at Library/PackageCache/com.unity.textmeshpro@3.0.6/Scripts/Runtime/TMPro_UGUI_Private.cs:1670)
TMPro.TextMeshProUGUI.Rebuild (UnityEngine.UI.CanvasUpdate update) (at Library/PackageCache/com.unity.textmeshpro@3.0.6/Scripts/Runtime/TextMeshProUGUI.cs:216)
UnityEngine.UI.CanvasUpdateRegistry.PerformUpdate () (at Library/PackageCache/com.unity.ugui@1.0.0/Runtime/UI/Core/CanvasUpdateRegistry.cs:217)
UnityEngine.Canvas:SendWillRenderCanvases()