Algorithms that Override Process Groups Do Not Report Errors When Called From Algorithm Dialog

[cailafinn]

Describe the bug
When an algorithm is called with a group workspace it will make a call to processGroups(). For most algorithms, this will just run the algorithm on every individual workspace in the group.

However, if you want to actually process groups specially, this method is overridden. This seems to cause a bug where throwing an error results in nothing being sent to the message log. This can be very confusing as you only get the "AlgName Started" message and nothing more.

Strangely, this only occurs when the algorithm is called from the dialog. Calling the algorithm in a script causes it to act as you would expect.

To Reproduce

1. Load/Create a group workspace
2. Open the SaveNexusESS dialog (it doesn't have to be this, it's just a convenient example).
3. Provide the group workspace as an input
4. Run the algorithm.
5. Nothing will happen.

Expected behavior
Any errors produced should be seen in the messages log.

Platform/Version (please complete the following information):

• OS: Seen on macOS and Windows, assume all.
• Mantid Version: At least as early as 6.7