Clear 'thumbnailError' when uploading new one

## Issue
"thumbnail is invalid" not reset with new thumbnail upload #6044
https://github.com/lbryio/lbry-desktop/issues/6044

## Change
The previous PR only covered the scenario of changing between NEW and EDIT. This one covers "uploading new".

dist/bundle.es.js

@@ -4634,7 +4634,8 @@ const doResetThumbnailStatus = () => dispatch => {
   dispatch({
     type: UPDATE_PUBLISH_FORM,
     data: {
-      thumbnailPath: ''
+      thumbnailPath: '',
+      thumbnailError: undefined
     }
   });
 
@@ -4691,6 +4692,13 @@ const doUploadThumbnail = (filePath, thumbnailBlob, fsAdapter, fs, path) => disp
     }, doError(error)));
   };
 
+  dispatch({
+    type: UPDATE_PUBLISH_FORM,
+    data: {
+      thumbnailError: undefined
+    }
+  });
+
   const doUpload = data => {
     return fetch(SPEECH_PUBLISH, {
       method: 'POST',

src/redux/actions/publish.js

@@ -21,6 +21,7 @@ export const doResetThumbnailStatus = () => (dispatch: Dispatch) => {
     type: ACTIONS.UPDATE_PUBLISH_FORM,
     data: {
       thumbnailPath: '',
+      thumbnailError: undefined,
     },
   });
 
@@ -96,6 +97,13 @@ export const doUploadThumbnail = (
     );
   };
 
+  dispatch({
+    type: ACTIONS.UPDATE_PUBLISH_FORM,
+    data: {
+      thumbnailError: undefined,
+    },
+  });
+
   const doUpload = data => {
     return fetch(SPEECH_PUBLISH, {
       method: 'POST',