py: Change vstr so that it doesn't null terminate buffer by default.

This cleans up vstr so that it's a pure "variable buffer", and the user
can decide whether they need to add a terminating null byte.  In most
places where vstr is used, the vstr did not need to be null terminated
and so this patch saves code size, a tiny bit of RAM, and makes vstr
usage more efficient.  When null termination is needed it must be
done explicitly using vstr_null_terminate.

1 files changed, 1 insertions, 0 deletions

diff --git a/teensy/main.c b/teensy/main.c
index 082f6f1ca9..34a804c60a 100644
--- a/teensy/main.c
+++ b/teensy/main.c
@@ -319,6 +319,7 @@ soft_reset:
         } else {
             vstr_add_str(vstr, mp_obj_str_get_str(pyb_config_main));
         }
+        vstr_null_terminate(vstr);
         if (!pyexec_file(vstr_str(vstr))) {
             flash_error(3);
         }