BUG: Support ndim=0 when constructing arrays from buffer

Previously the buffer was interpreted as 1-dimensional when
no shape was provided, even when ndim was 0.

Closes gh-4015
BUG: Fix raising exception on invalid assignment from sequence

Closes gh-4024
Merge pull request #4024 from eltjpm/from_sequence_fix

Sequence assignment doesn't raise exception on shape mismatch