OSMessageBoxWin32 shows message box behind the viewer window

[LLGuru]

Environment

SecondLife viewer any win64 build

Description

In some cases (e.g., runtime error message and user click the window) OSMessageBoxWin32 shows message box behind the viewer window

As a result, the user doesn't see this message box and can't interact with it until switches between windows

Reproduction steps

• Start viewer
• Double click top menu Develop | Force an Error | Force LLError And Crash

[LLGuru]

• Fixed in https://github.com/secondlife/viewer/pull/2031

[AtlasLinden]

Reopening for testing

[valeriiaaproductengine]

Passed QA. Verified on the Second Life Release 7.1.10.10582490681 (64bit) on Win10/OSX in the scope of https://github.com/secondlife/iqa/issues/316.