Fix crash when saving compressed image as JPG & WebP

modules/jpg/image_loader_jpegd.cpp

@@ -156,7 +156,11 @@ public:
 
 static Error _jpgd_save_to_output_stream(jpge::output_stream *p_output_stream, const Ref<Image> &p_img, float p_quality) {
 	ERR_FAIL_COND_V(p_img.is_null() || p_img->is_empty(), ERR_INVALID_PARAMETER);
-	Ref<Image> image = p_img;
+	Ref<Image> image = p_img->duplicate();
+	if (image->is_compressed()) {
+		Error error = image->decompress();
+		ERR_FAIL_COND_V_MSG(error != OK, error, "Couldn't decompress image.");
+	}
 	if (image->get_format() != Image::FORMAT_RGB8) {
 		image->convert(Image::FORMAT_RGB8);
 	}

modules/webp/webp_common.cpp

@@ -59,6 +59,10 @@ Vector<uint8_t> _webp_packer(const Ref<Image> &p_image, float p_quality, bool p_
 	compression_method = CLAMP(compression_method, 0, 6);
 
 	Ref<Image> img = p_image->duplicate();
+	if (img->is_compressed()) {
+		Error error = img->decompress();
+		ERR_FAIL_COND_V_MSG(error != OK, Vector<uint8_t>(), "Couldn't decompress image.");
+	}
 	if (img->detect_alpha()) {
 		img->convert(Image::FORMAT_RGBA8);
 	} else {