fixed zero-sized buffer condition check

buffer.go

@@ -42,7 +42,9 @@ func (b *Buffer[T]) y(y int) int {
 
 // Set sets the value at position (x,y) to c
 func (b *Buffer[T]) Set(x, y int, v T) {
-	b.data[b.y(y)][b.x(x)] = v
+	if b.width > 0 && b.height > 0 {
+		b.data[b.y(y)][b.x(x)] = v
+	}
 }
 
 // Get returns the value at position (x,y)
@@ -102,8 +104,8 @@ func (b *Buffer[T]) Sub(x, y, w, h int) *Buffer[T] {
 	// sanitize inputs
 	x = limit(x, 0, b.width-1)
 	y = limit(y, 0, b.height-1)
-	w = limit(w, 1, b.width-x)
-	h = limit(h, 1, b.height-y)
+	w = limit(w, 0, b.width-x)
+	h = limit(h, 0, b.height-y)
 
 	// make slice references
 	data := make([][]T, h)

buffer_test.go

@@ -17,3 +17,8 @@ func TestSub(t *testing.T) {
 	fmt.Println(strings.Repeat("-", 10))
 	fmt.Println(s)
 }
+
+func TestSet(t *testing.T) {
+	b := NewBuffer(0, 0, ' ')
+	b.Set(0, 0, 'a')
+}