Markdown: Don't crash on files with html images, alt text, inside links
If we have code like 
and the img has alt text
The old code did remove image insert alt text but when we remove the image, the qtextdocument says "i don't need the anymore since there's nothing inside" and then everything breaks because the layout has changed and we're iterating over "unexisting" text blocks
So instead we just insert the alt text and since we have selected the image with the cursor it will replace it correctly