Guaranteeing good stacktraces from portable mode users on Windows by forcing presence of pdb file

[FranciscoPombal]

Copied over from #14505 (comment):

Since apparently quite a few users make use of portable mode, should we prevent qBittorrent from starting if the pdb is not present in the same directory as the executable (only applicable on Windows, of course)? I suspect that when many users prepare a "portable" installation (e.g. in a USB drive), they only copy over the executable, not the pdb. Thus, forcing users to hold on to the pdb would result in usable crash reports from them as well.
The check can be really simple: just check if there is a file with the expected name in the same directory; if not, display an error message and exit.

Thoughts?