Fix no error-msg when a plugin download failed

[xomx]

Fix #95
Fix notepad-plus-plus/notepad-plus-plus#17044

[xomx]

@donho
IDK if you've already noticed this PR?

I'm trying to fix this as I've already experienced a situation when I tried to install a plugin via PluginsAdmin but nothing happened after the N++ restart. Later I discovered that my plugin-zip downloading failed somehow (FW, net error or similar) but there wasn't a single msg about, so I tried unsuccessfully several times before I figured out what was going on...

The fix is simple but I'm not sure if the original bool isSilentMode true in:

wingup/src/winmain.cpp

Line 1355 in 66f652d

bool isSuccessful = downloadBinary(dlUrl, dlDest, sha256ToCheck, pair<wstring, int>(extraOptions.getProxyServer(), extraOptions.getPort()), true, pair<wstring, wstring>(dlStopped, gupParams.getMessageBoxTitle()));

was not there for a deeper reason that I didn't see?

[donho]

@xomx
Oups! Sorry, I didn't see it at all. You have done the right thing to ping me.