Show predictions in the right cases (A58)

After reverting an auto-correct we always have a separator after
the previously inserted word, and the cursor is never touching
a word. Showing predictions is the right thing to do, while
calling postUpdateSuggestions will invariably yield an invariably
blank suggestion strip, which is not very helpful.

Likewise, after we pick a suggestion, we should be showing the
predictions unless showing the addToDictionary hint. There was
a bug here in the corner case that the word would be a candidate
for user dictionary, but the user dictionary provider is not
available: in this case we should be showing predictions, but
we were showing an unhelpful empty suggestion bar.

Change-Id: I287bb5eb4af762bd5a433e85e185fab6d203e91a