check that image bit depth is supported by Kvazaar (#1384)

libheif/plugins/encoder_kvazaar.cc

@@ -375,8 +375,11 @@ static struct heif_error kvazaar_encode_image(void* encoder_raw, const struct he
   bool isGreyscale = (heif_image_get_colorspace(image) == heif_colorspace_monochrome);
   heif_chroma chroma = heif_image_get_chroma_format(image);
 
-  const kvz_api* api = kvz_api_get(bit_depth);
-  if (api == nullptr) {
+  // Kvazaar uses a hard-coded bit depth (https://github.com/ultravideo/kvazaar/issues/399).
+  // Check whether this matches to the image bit depth.
+  // TODO: we should check the bit depth supported by the encoder (like query_input_colorspace2()) and output a warning
+  //       if we have to encode at a different bit depth than requested.
+  if (bit_depth != KVZ_BIT_DEPTH) {
     struct heif_error err = {
         heif_error_Encoder_plugin_error,
         heif_suberror_Unsupported_bit_depth,
@@ -385,6 +388,16 @@ static struct heif_error kvazaar_encode_image(void* encoder_raw, const struct he
     return err;
   }
 
+  const kvz_api* api = kvz_api_get(bit_depth);
+  if (api == nullptr) {
+    struct heif_error err = {
+        heif_error_Encoder_plugin_error,
+        heif_suberror_Unspecified,
+        "Could not initialize Kvazaar API"
+    };
+    return err;
+  }
+
   auto uconfig = make_guard(api->config_alloc(), [api](kvz_config* cfg) { api->config_destroy(cfg); });
   kvz_config* config = uconfig.get();
   api->config_init(config); // param, encoder->preset.c_str(), encoder->tune.c_str());