fix empty pattern duration calculation.

src/context/Patterns.tsx

@@ -117,7 +117,7 @@ export function totalDuration(pattern: Pattern): number {
   return reduce(
     pattern.pulses,
     (former, pulse) => former + pulse.offset,
-    pattern.smoothRepeat ? 100 : 0,
+    pattern.smoothRepeat && pattern.pulses.length > 1 ? 100 : 0,
   );
 }