more generic HasVSIHandler

it covers the case where prefix is in handlers but handler is nil

Co-authored-by: Thomas Bonfort <thomas.bonfort@airbus.com>

godal.go

@@ -3903,8 +3903,8 @@ func HasVSIHandler(prefix string) bool {
 	if handlers == nil {
 		return false
 	}
-	_, ok := handlers[prefix]
-	return ok
+	handler, ok := handlers[prefix]
+	return ok && handler.KeySizerReaderAt != nil
 }
 
 // BuildVRT runs the GDALBuildVRT function and creates a VRT dataset from a list of datasets

godal_test.go

@@ -3459,17 +3459,31 @@ func (mvp mvpHandler) ReadAtMulti(k string, buf [][]byte, off []int64) ([]int, e
 	}
 	return b.(KeyMultiReader).ReadAtMulti(k, buf, off)
 }
+func TestHasVSIHandler(t *testing.T) { // stripPrefix false
+	assert.False(t, HasVSIHandler("prefix://"))
+
+	vpa := vpHandler{datas: make(map[string]KeySizerReaderAt)}
+	err := RegisterVSIHandler("prefix://", vpa, VSIHandlerStripPrefix(false))
+	assert.NoError(t, err)
+	assert.True(t, HasVSIHandler("prefix://"))
+
+	// nil handler
+	err = RegisterVSIHandler("nil_prefix://", nil)
+	assert.NoError(t, err)
+	assert.False(t, HasVSIHandler("nil_prefix://"))
+
+	// unregistered_prefix
+	assert.False(t, HasVSIHandler("unregistered_prefix://"))
+}
 
 func TestVSIPrefix(t *testing.T) {
 	tifdat, _ := ioutil.ReadFile("testdata/test.tif")
 
-	assert.False(t, HasVSIHandler("prefix://"))
 	// stripPrefix false
 	vpa := vpHandler{datas: make(map[string]KeySizerReaderAt)}
 	vpa.datas["prefix://test.tif"] = mbufHandler{tifdat}
 	err := RegisterVSIHandler("prefix://", vpa, VSIHandlerStripPrefix(false))
 	assert.NoError(t, err)
-	assert.True(t, HasVSIHandler("prefix://"))
 
 	ds, err := Open("prefix://test.tif")
 	if err != nil {