[SPARK-14739][PYTHON][ML]

[zero323]

What changes were proposed in this pull request?

Fix parsing empty dense and sparse vectors, correct dead parsing tests.

How was this patch tested?

Fixed parsing tests, added tests specific to SPARK-14739

[SparkQA]

Test build #56297 has finished for PR 12511 at commit be9809a.

• This patch fails Python style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #56301 has finished for PR 12511 at commit fb8e615.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.