fix: verify if the path starts with /

add a condition to verify if the path already starts with /, so we must not add another one

fixes issue decaporg#5569

packages/netlify-cms-core/src/components/MediaLibrary/MediaLibraryButtons.js

@@ -90,7 +90,7 @@ export class CopyToClipBoardButton extends React.Component {
   handleCopy = () => {
     clearTimeout(this.timeout);
     const { draft, name } = this.props;
-    const path = `/${this.props.path}`;
+    const path = this.props.path.charAt(0) !== '/' ? `/${this.props.path}` : this.props.path;
     copyToClipboard(isAbsolutePath(path) || !draft ? path : name);
     this.setState({ copied: true });
     this.timeout = setTimeout(() => this.mounted && this.setState({ copied: false }), 1500);