Fix bug where PyBuffer_Release is called after a Python error is raised

Caught by the debug build of the Python 3.4 interpreter. In the ft_render.c
function _PGFT_Render_Array, PgBuffer_Release was called if
_validate_view_format() raised an exception. BgBuffer_Release in turn calls
PyBuffer_Release. PyBuffer_Release expects no pending errors, as checked by
a C assert.

The change raises the exception after the buffer is freed by PgBuffer_Release.
The error message is still built before the PgBuffer_Release call.
merge in unintensional branch