[fuchsia] Check if InputEvent is null in IME's DidUpdateState

DidUpdateState can be null if there is no key associated with a state
update. In these cases, since we only care about extracting the keypress
associated with edits, we can just ignore the DidUpdateState call and
return early.

Change-Id: I5a6ce0a5ef13b8afad89abf6dab3eaf39167e74a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1573083
Commit-Queue: Robert Lord <lard@google.com>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652376}

ui/base/ime/fuchsia/input_method_fuchsia.cc

@@ -89,6 +89,13 @@ void InputMethodFuchsia::OnBlur() {
 void InputMethodFuchsia::DidUpdateState(
     fuchsia::ui::input::TextInputState state,
     std::unique_ptr<fuchsia::ui::input::InputEvent> input_event) {
+  // The FIDL protocol for DidUpdateState allows it to be null, and so we may
+  // receive state updates that have no associated key. Since we're only
+  // interested in extracting out input events from this stream for now, we can
+  // just ignore state updates with no input event.
+  if (!input_event)
+    return;
+
   if (input_event->is_keyboard())
     event_converter_.ProcessEvent(*input_event);
   else