opts: fix potential panic in trimQuotes

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

opts/quotedstring.go

@@ -22,6 +22,9 @@ func (s *QuotedString) String() string {
 }
 
 func trimQuotes(value string) string {
+	if len(value) < 2 {
+		return value
+	}
 	lastIndex := len(value) - 1
 	for _, char := range []byte{'\'', '"'} {
 		if value[0] == char && value[lastIndex] == char {

opts/quotedstring_test.go

@@ -28,3 +28,13 @@ func TestQuotedStringSetWithNoQuotes(t *testing.T) {
 	assert.NilError(t, qs.Set("something"))
 	assert.Check(t, is.Equal("something", qs.String()))
 }
+
+func TestQuotedStringShort(t *testing.T) {
+	value := ""
+	qs := NewQuotedString(&value)
+	assert.NilError(t, qs.Set(`"`))
+	assert.Check(t, is.Equal(`"`, qs.String()))
+
+	assert.NilError(t, qs.Set(`'`))
+	assert.Check(t, is.Equal(`'`, qs.String()))
+}