B02005 - Boulder and vision followup

put back code to remove LAUNCH_UNSEEN from the mask that got lost
when I re-arranged the change.

src/trap.c

@@ -1280,6 +1280,7 @@ int style;
 				     "someone bowling." :
 				     "rumbling in the distance.");
 			}
+			style &= ~LAUNCH_UNSEEN;
 			goto roll;
 	    case ROLL|LAUNCH_KNOWN:
 			/* use otrapped as a flag to ohitmon */