python.pkgs.wrapPython: fix string makeWrapperArgs

Bash takes an assignment of a string to an array variable:

local -a user_args
user_args="(foo bar)"

to mean appending the string to the array, not parsing the string into
an array as is the case when on the same line as the declaration:

local -a user_args="(foo bar)"

b0633406 extracted the declaration before
the newly branched code block, causing string makeWrapperArgs being added
to the array verbatim.

Since local is function scoped, it does not matter if we move it inside
each of the branches so we fix it this way.