[smartredraw] Fix dialog progress not being updated

[enen92]

Description

This fixes progress dialogs not being updated if smartredraw is enabled. If the new percentage differs from the old/stored one, the dialog must be refreshed (dirtyregions set).

Motivation and context

Fix #15354

How has this been tested?

With the video download functionality provided by the Aerial screensaver

What is the effect on users?

DialogProgress should behave decently if smartredraw is enabled

Screenshots (if appropriate):

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed