mqbscan: exit if no sync found

mqbscan.c

@@ -192,10 +192,9 @@ int main(int argc, char **argv)
 		init_bits(&fb);
 		fb.fill_bits = fill_bits_mqb;
 
-		find_sync(&br, MQB_MARKER, 56, 1024);
-
-		for (;;)
-			print_mqb_frame(&fb);
+		if (!find_sync(&br, MQB_MARKER, 56, 1024))
+			for (;;)
+				print_mqb_frame(&fb);
 	}
 
 	sf_close(file);