fix(textinput): slicing outside cap (#532)

* textinput: fix slicing outside cap

* textinput: add test that makes slicing outside cap occur

* chore: tidy with gofmt

---------

Co-authored-by: bashbunni <bunni@bashbunni.dev>

textinput/textinput_test.go

@@ -30,3 +30,10 @@ func Test_CurrentSuggestion(t *testing.T) {
 		t.Fatalf("Error: expected first suggestion but was %s", suggestion)
 	}
 }
+
+func Test_SlicingOutsideCap(t *testing.T) {
+	textinput := New()
+	textinput.Placeholder = "作業ディレクトリを指定してください"
+	textinput.Width = 32
+	textinput.View()
+}