Add image paste fallback

Fixes Firefox pasting support
(and possibly other browsers)

javascript/dragdrop.js

@@ -9,11 +9,19 @@ function dropReplaceImage( imgWrap, files ) {
         return;
     }
 
+    const tmpFile = files[0];
+
     imgWrap.querySelector('.modify-upload button + button, .touch-none + div button + button')?.click();
     const callback = () => {
         const fileInput = imgWrap.querySelector('input[type="file"]');
         if ( fileInput ) {
-            fileInput.files = files;
+            if ( files.length === 0 ) {
+                files = new DataTransfer();
+                files.items.add(tmpFile);
+                fileInput.files = files.files;
+            } else {
+                fileInput.files = files;
+            }
             fileInput.dispatchEvent(new Event('change'));   
         }
     };