[CLI] Analyze command does not create the XML output file and returns incorrect exit code when only compiler diagnostics are reported

[PeterKaszab]

Product and Version Used:
Roslynator.DotNet.Cli 0.5.0

Steps to Reproduce:
Create a new console project, and place the following code to Program.cs

int a, b = 1, 0;
Console.WriteLine(a);

Then, run roslynator analyze -o out.xml on the previously created project.

Actual Behavior:

• CS0219 is reported, but out.xml is not created.
• If the output also contains analyzer diagnostics, then out.xml created and contains both analyzer and compiler diagnostics.
• Exit code is 0

Expected Behavior:
out.xml should be created even if it only contains compiler diagnostics.

• Exit code should be 1

[PeterKaszab]

Note: this is really similar to #963, which is already fixed by #964.