'List Schedules on Sheets' has error if there aren't any schedules on sheets

[RevitIRL]

Describe the bug
'List Schedules on Sheets' has error if there aren't any schedules on sheets

To Reproduce
Steps to reproduce the behavior:

1. In a project with no schedules on sheets
2. Drawing Set > Schedules > List Schedules on Sheets
3. See error

Expected behavior
A dialog similar to 'List Legends on Sheets':

Screenshots

Desktop (please complete the following information):

• OS: Windows 10 Pro
• pyRevit Version 4.8.13.23076+1737 (wip; 2023-03-17)
• pyRevit Environment:

(c) Microsoft Corporation. All rights reserved.

C:\Users\...>pyrevit env
==> Registered Clones (full git repos)
==> Registered Clones (deployed from archive/image)
master | Deploy: "basepublic" | Branch: "master" | Version: "4.8.13.23076+1737-wip" | Path: "C:\Users\...\AppData\Roaming\pyRevit-Master"
==> Attachments
master | Product: "2023 First Customer Ship" | Engine: IPY277 (277) | Path: "C:\Users\...\AppData\Roaming\pyRevit-Master"
master | Product: "2022.1.3" | Engine: IPY277 (277) | Path: "C:\Users\...\AppData\Roaming\pyRevit-Master" 
master | Product: "2021.1.6" | Engine: IPY277 (277) | Path: "C:\Users\...\AppData\Roaming\pyRevit-Master" 
master | Product: "2020.2.7" | Engine: IPY277 (277) | Path: "C:\Users\...\AppData\Roaming\pyRevit-Master" 
master | Product: "2019.2.5" | Engine: IPY277 (277) | Path: "C:\Users\...\AppData\Roaming\pyRevit-Master" 
master | Product: "2018.3.3 Security Fix" | Engine: IPY277 (277) | Path: "C:\Users\...\AppData\Roaming\pyRevit-Master"
==> Installed Extensions
==> Default Extension Search Path
C:\Users\...\AppData\Roaming\pyRevit\Extensions
==> Extension Search Paths
==> Extension Sources - Default
https://github.com/eirannejad/pyRevit/raw/master/extensions/extensions.json
==> Extension Sources - Additional
==> Installed Revits
2023 First Customer Ship | Version: 23.0.1.318 | Build: 20220304_1515(x64) | Language: 1033 | Path: "C:\Program Files\Autodesk\Revit 2023\"
2022.1.3 | Version: 22.1.30.34 | Build: 20220520_1515(x64) | Language: 1033 | Path: "C:\Program Files\Autodesk\Revit 2022\"
2021.1.6 | Version: 21.1.60.25 | Build: 20220123_1515(x64) | Language: 1033 | Path: "C:\Program Files\Autodesk\Revit 2021\"
2020.2.7 | Version: 20.2.70.6 | Build: 20220112_1230(x64) | Language: 1033 | Path: "C:\Program Files\Autodesk\Revit 2020\"
2019.2.5 | Version: 19.2.50.16 | Build: 20220111_1110(x64) | Language: 1033 | Path: "C:\Program Files\Autodesk\Revit 2019\"
2018.3.3 Security Fix | Version: 18.3.3.18 | Build: 20190510_1515(x64) | Language: 1033 | Path: "C:\Program Files\Autodesk\Revit 2018\"
==> Running Revit Instances
PID: 49500 | 2022.1.3 | Version: 22.1.30.34 | Build: 20220520_1515(x64) | Language: 0 | Path: "C:\Program Files\Autodesk\Revit 2022"
PID: 13836 | 2018.3.3 Security Fix | Version: 18.3.3.18 | Build: 20190510_1515(x64) | Language: 0 | Path: "C:\Program Files\Autodesk\Revit 2018"
==> User Environment
Microsoft Windows 10 [Version 10.0.19044]
Executing User: ...
Active User: ...
Admin Access: No
%APPDATA%: "C:\Users\...\AppData\Roaming"
Latest Installed .Net Framework: 4.8
Installed .Net Target Packs: v3.5 v4.0 v4.5 v4.5.1 v4.5.2 v4.6 v4.6.1 v4.6.2 v4.7 v4.7.1 v4.7.2 v4.8 v4.X
Installed .Net-Core Target Packs: v5.0.400
pyRevit CLI v4.8.13.23076+1737-wip

C:\Users\...>

Additional context
#1702

[jmcouffin]

fixed by #1768