Unnecessary error window appears when UTbot fails to generate test #980

Description
When test generation fails UTBot shows two error messages while one is enough.
"Failed to save tests report" is unneeded when test generation fails.

To Reproduce
Try to generate tests for some class with Test generation timeout = 1

Expected behavior
Only one error message shown.

Actual behavior
Two error messages appeared one after another. second one looks unnecessary, knowing that generation failed.