Improve textarea paste (#31948)

- When pasting a URL over another URL, replace the URL instead of
creating a useless `[url](url)`. This is the 1-line change
[here](https://github.com/go-gitea/gitea/pull/31948/files#diff-be8e94d7e3da33b187381f53d28095107bd0cf29ae9a9e997e4f422f4a54479cR122).
- Always run `initTextareaEvents`, previously it was not run when
`dropzoneEl` was not present like when attachements are disabled on the
server. Refactored the function to gracefully handle absent `dropzoneEl`
and rename the function to a better name.

web_src/js/features/comp/EditorUpload.ts

@@ -119,7 +119,7 @@ function handleClipboardText(textarea, e, {text, isShiftDown}) {
   const {value, selectionStart, selectionEnd} = textarea;
   const selectedText = value.substring(selectionStart, selectionEnd);
   const trimmedText = text.trim();
-  if (selectedText && isUrl(trimmedText)) {
+  if (selectedText && isUrl(trimmedText) && !isUrl(selectedText)) {
     e.preventDefault();
     replaceTextareaSelection(textarea, `[${selectedText}](${trimmedText})`);
   }
@@ -156,7 +156,7 @@ export function initEasyMDEPaste(easyMDE, dropzoneEl) {
   });
 }
 
-export function initTextareaUpload(textarea, dropzoneEl) {
+export function initTextareaEvents(textarea, dropzoneEl) {
   let isShiftDown = false;
   textarea.addEventListener('keydown', (e) => {
     if (e.shiftKey) isShiftDown = true;
@@ -166,7 +166,7 @@ export function initTextareaUpload(textarea, dropzoneEl) {
   });
   textarea.addEventListener('paste', (e) => {
     const {images, text} = getPastedContent(e);
-    if (images.length) {
+    if (images.length && dropzoneEl) {
       handleUploadFiles(new TextareaEditor(textarea), dropzoneEl, images, e);
     } else if (text) {
       handleClipboardText(textarea, e, {text, isShiftDown});
@@ -176,7 +176,7 @@ export function initTextareaUpload(textarea, dropzoneEl) {
     if (!e.dataTransfer.files.length) return;
     handleUploadFiles(new TextareaEditor(textarea), dropzoneEl, e.dataTransfer.files, e);
   });
-  dropzoneEl.dropzone.on(DropzoneCustomEventRemovedFile, ({fileUuid}) => {
+  dropzoneEl?.dropzone.on(DropzoneCustomEventRemovedFile, ({fileUuid}) => {
     const newText = removeAttachmentLinksFromMarkdown(textarea.value, fileUuid);
     if (textarea.value !== newText) textarea.value = newText;
   });