libluna: Do not sort empty arrays; avoids a segfault

libluna/src/Sort.cpp

@@ -50,5 +50,6 @@ static void quicksort_impl(void* base, usize start, usize end, usize size, compa
 
 void c_quicksort(void* base, usize nmemb, usize size, compar_t compar)
 {
+    if (nmemb == 0) return;
     quicksort_impl(base, 0, nmemb - 1, size, compar);
 }