nk_textedit_paste will try to insert even if edit.mode is NK_TEXT_EDIT_MODE_REPLACE

[StewBC]

Pasting into an nk_edit_string will end up in nk_str_insert_at_char which, if the edit buffer is at capacity, will fail since an insert is not possible. But, if the edit mode is NK_TEXT_EDIT_MODE_REPLACE, the characters in the edit buffer should be replaced by the pasted characters (up to max capacity) and the call should not simply fail.