engine: Korean and Telex let Enter and Tab through after committing

Enter with a pending syllable committed it and stopped there, so a chat
message needed Enter twice; Korean input methods commit and pass the key
on. Japanese keeps consuming the key that confirms a reading or a chosen
candidate, as Japanese input methods do.

README.md

@@ -19,9 +19,11 @@ Vietnamese Telex is also available as a compatibility mode.
 Use `Up`/`Down` to move through candidates and `PageUp`/`PageDown` to move by
 nine without wrapping. An unmodified `1`-`9` selects that row on the current
 page. `Enter` and `Tab` commit a candidate you have moved to; otherwise they
-commit the reading, as `0` always does. In a temporary Emoji or Hanja search,
-`Enter` commits the highlighted result and `Tab`/`Shift-Tab` wrap through
-the results. `Esc` cancels composition.
+commit the reading, as `0` always does. Japanese consumes the confirming key;
+Korean and Vietnamese pass it on to the application. In a temporary Emoji or
+Hanja search, `Enter` commits the highlighted result and `Tab`/`Shift-Tab`
+wrap through the results. Leaving the field or clicking elsewhere commits
+what is pending; `Esc` cancels it.
 
 Hiragana mode composes a complete reading before offering Kanji candidates.
 Katakana mode does not perform Kanji conversion. Emoji and Hanja searches