Fix music not being silent during trinket/crewmate collect

Looks like I forgot to test that my music silencing patch didn't break
the music being silent during the "You have found a shiny trinket" and
"You have found a shiny crewmate" text boxes. So I've added a check for
game.completestop in the music handling in main.cpp.

Found this bug while I was testing my towerlogic/gamelogic merge patch.

desktop_version/src/main.cpp

@@ -541,7 +541,7 @@ int main(int argc, char *argv[])
         {
             Mix_Volume(-1,MIX_MAX_VOLUME);
 
-            if (game.musicmuted)
+            if (game.musicmuted || game.completestop)
             {
                 Mix_VolumeMusic(0);
             }