Patch to workaround biblatex oddities with the natbib option in versions < 3.5

patch_biblatex.sty

% biblatex authoryear with natbib does a million stray commas in versions < 3.5
% see: https://tex.stackexchange.com/q/312539/
% this works around it for versions 3.3 and 3.4
\ifthenelse{\equal{\abx@version}{3.4}}{%
    \DeclareDelimFormat[cbx@textcite]{nameyeardelim}{\addspace}
}{\ifthenelse{\equal{\abx@version}{3.3}}{%
    % Workaround following http://golatex.de/neue-biber-version-ploetzlich-komma-bei-zitierung-t17005.html
    % (in German...), which changes \nameyeardelim / \nonameyeardelim to \addspace
    % in the citation style's textcite macro.
    % sigh....
	\renewbibmacro*{textcite}{% 
        \ifnameundef{labelname}
          {\iffieldundef{shorthand}
             {\usebibmacro{cite:label}%
              \setunit{%
                \global\booltrue{cbx:parens}%
                \addspace\bibopenparen}%  This was changed
              \ifnumequal{\value{citecount}}{1}
                {\usebibmacro{prenote}}
                {}%
              \usebibmacro{cite:labelyear+extrayear}}
             {\usebibmacro{cite:shorthand}}}
          {\printnames{labelname}%
           \setunit{%
             \global\booltrue{cbx:parens}%
             \addspace\bibopenparen}%
           \ifnumequal{\value{citecount}}{1}
             {\usebibmacro{prenote}}
             {}%
           \usebibmacro{citeyear}}}
}{%
    % version is not 3.3 or 3.4; assuming we're good :)
}}