Images broken if previewing a Post without updating it first

[ngoctr]

Describe the bug
While we were working on this, we had noticed an issue where previewing in the Block Editor while images being uploaded: Ref #13910 (review)

To Reproduce
Steps to reproduce the behavior:

1. From WordPress app, Go to Site -> Posts then select a Post to edit. Switch to Block Editor if you're on the classic editor.
2. Add an Image block, then tap ADD IMAGE and choose Free Photo Library
3. Search and select an image of your choice
4. While the image being uploaded, Tap the ... menu at the top-right corner, select Preview, you will the image being broken.

Expected behavior
In my opinion, since the image has not been uploaded yet so the preview won't be able to show the image. However, the Preview button is there, and it user would expect to see images when previewing a Post.

Screenshots

Smartphone (please complete the following information):

• Device: [iPhone, iPad]
• OS: [iOS]
• Version [13.4]

Additional context
N/A

[maxme]

In my opinion, since the image has not been uploaded yet so the preview won't be able to show the image. However, the Preview button is there, and it user would expect to see images when previewing a Post.

I agree. In wpandroid (with classic or the block editor), we show a toast message ("You are currently uploading media. Please wait until this completes.") when the Preview button is pressed during an image upload.

Ref. https://github.com/wordpress-mobile/WordPress-Android/blob/a3988b1b990862b2e7ee16df6737c449a43349f1/WordPress/src/main/java/org/wordpress/android/ui/posts/EditPostActivity.java#L1112

I think the same behavior should be implemented on wpios (I thought this was part of the preview revamp project cc @diegoreymendez @yaelirub)

[yaelirub]

Thanks @maxme ! I'll add this to our backlog