py/objstr: Avoid double zero init on sized bytes.

As per the implementation of m_malloc0, if
MICROPY_GC_CONSERVATIVE_CLEAR is set then all RAM is guaranteed to be
zero-init by gc_alloc.

py/objstr.c: Guard the explicit zero init in bytes_make_new
against being run, initialising the RAM to zero a second time, if this
flag is set.

Signed-off-by: Phil Howard <github@gadgetoid.com>

Author: Gadgetoid

py/objstr.c

@@ -282,7 +282,10 @@ static mp_obj_t bytes_make_new(const mp_obj_type_t *type_in, size_t n_args, size
         }
         vstr_t vstr;
         vstr_init_len(&vstr, len);
+        // If this config is set then the GC clears all memory, so we don't need to.
+        #if !MICROPY_GC_CONSERVATIVE_CLEAR
         memset(vstr.buf, 0, len);
+        #endif
         return mp_obj_new_bytes_from_vstr(&vstr);
     }