InputText: fix 'number' hint (#9362)
InputText: fix 'number' hint (#9362)

When input_type == "number" convert the hint to "string" type.
Closes #9359.
NiLuJe/koreader,koreader/koreader,poire-z/koreader,Frenzie/koreader,NiLuJe/koreader,poire-z/koreader,Frenzie/koreader,koreader/koreader