Fixed: Built-in updater for mono version

The change to set ExecutingApplication in 26a04c9fd broke mono - it
returned the location of the mono executable and not radarr.

It seems that there was a change in behaviour in net5.0 which means we
can no longer use the same code in both cases.

src/NzbDrone.Common/EnvironmentInfo/RuntimeInfo.cs

@@ -23,7 +23,10 @@ namespace NzbDrone.Common.EnvironmentInfo
                                serviceProvider.ServiceExist(ServiceProvider.SERVICE_NAME) &&
                                serviceProvider.GetStatus(ServiceProvider.SERVICE_NAME) == ServiceControllerStatus.StartPending;
 
-            //Guarded to avoid issues when running in a non-managed process
+#if NETCOREAPP
+            // net5.0 will return Radarr.dll for entry assembly, we need the actual
+            // executable name (Radarr on linux).  On mono this will return the location of
+            // the mono executable itself, which is not what we want.
             var entry = Process.GetCurrentProcess().MainModule;
 
             if (entry != null)
@@ -31,6 +34,12 @@ namespace NzbDrone.Common.EnvironmentInfo
                 ExecutingApplication = entry.FileName;
                 IsWindowsTray = OsInfo.IsWindows && entry.ModuleName == $"{ProcessProvider.RADARR_PROCESS_NAME}.exe";
             }
+#else
+            // On mono we need to get the location of the Radarr assembly, not Mono.
+            // Can't be running tray app in mono.
+            ExecutingApplication = Assembly.GetEntryAssembly()?.Location;
+#endif
+
         }
 
         static RuntimeInfo()