Re-fetching signed-only message from API doesn't refresh the fetched text

[rrrooommmaaa]

To be implemented after PR #4144 and possibly refactor the decrypt-render-signature-... module interaction

[rrrooommmaaa]

These modules are calling each other in a complicated manner. Perhaps, a bit of refactoring is in order.

[tomholub]

reference #4144 (comment) - also check that we are not re-rendering text if we only just fetched new pubkeys