Treat the first space text character after a text:tab as significant whitespace

A space character is considered significant when it follows either a
non-space character element (e.g., text:tab), or a non-space character.

From the ODF specs (6.1.3, <text:s/>):
This element shall be used to represent the second and all following
“ “ (U+0020, SPACE) characters in a sequence of “ “ (U+0020, SPACE)
characters.
Merge pull request #203 from peitschie/insert-space-tab

Treat the first space text character after a text:tab as significant whitespace