[logging] USER null fallback (#3021)

If `USER` was unset, logging would crash immediately. `USER` is *not* a guaranteed variable, so to get around this we add a null fallback and also prefer `LOGNAME`, which is "standard" on POSIX systems (yet half the time isn't set because fuck me I guess)

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3021
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Reviewed-by: Maufeat <sahyno1996@gmail.com>

src/common/logging/backend.cpp

@@ -112,10 +112,20 @@ public:
             // This must be a static otherwise it would get checked on EVERY
             // instance of logging an entry...
             static std::string username = []() -> std::string {
-                auto* s = getenv("USER");
-                if (s == nullptr)
-                    s = getenv("USERNAME");
+                // in order of precedence
+                // LOGNAME usually works on UNIX, USERNAME on Windows
+                // Some UNIX systems suck and don't use LOGNAME so we also
+                // need USER :(
+                for (auto const var : {
+                         "LOGNAME",
+                         "USERNAME",
+                         "USER",
+                     }) {
+                    if (auto const s = getenv(var); s != nullptr)
                         return std::string{s};
+                }
+
+                return std::string{};
             }();
             if (!username.empty())
                 boost::replace_all(message, username, "user");