f_getenv/setenv: Access v_special when v_type is VAR_SPECIAL

Multiple Debian builds were failing these tests:

    Failures:
    	From test_environ.vim:
    	Found errors in Test_external_env():
    	function RunTheTest[37]..Test_external_env line 16: Expected '' but got 'FOO=null\n'
    	Found errors in Test_getenv():
    	function RunTheTest[37]..Test_getenv line 2: Expected v:null but got v:false
    	Found errors in Test_setenv():
    	function RunTheTest[37]..Test_setenv line 5: Expected v:null but got 'null'

This is because nvim has a separate tag (`v_special`) in `typval_T` for
special variables, whereas vim re-uses the `v_number` tag.

On little-endian architectures, using the incorrect tag is not an issue
because the byte representation is the same.  However, on big-endian
systems this caused the `v_number == kSpecialVarNull` checks to fail,
and the non-special code to execute.

0 files changed, 0 insertions, 0 deletions