engine: the Hanja search composes from its seed, and Escape gives it back

Ctrl+H took the pending syllable as the query, but the keys typed after
it started a composition of their own: gk, Ctrl+H, s showed 하ㄴ, and r,
Ctrl+H, k showed ㄱㅏ.  transstr now composes from a pending text, so
the search goes on where the syllable left off.  Escape ended the search
and dropped the syllable it had taken; it puts it back as pending text.

fn.h

@@ -31,7 +31,7 @@ void	popuplayout(Drawcmd*, int, int, Popup*);
 void	popupdraw(u32int*, Drawcmd*, Popup*);
 void	imthread(void*);
 void	impre(Im*, Str*);
-void	transstr(Lang*, Str*, Str*);
+void	transstr(Lang*, Str*, Str*, Str*);
 Emit	transmap(Im*, Rune);
 Emit	transko(Im*, Rune);
 Emit	transvi(Im*, Rune);