[SPARK-11084] [ML] [PYTHON] Check if index can contain non-zero value before binary search

At this moment `SparseVector.__getitem__` executes `np.searchsorted` first and checks if result is in an expected range after that. It is possible to check if index can contain non-zero value before executing `np.searchsorted`.

Author: zero323 <matthew.szymkiewicz@gmail.com>

Closes #9098 from zero323/sparse_vector_getitem_improved.