Spark 3.4: Fix NPE when create branch and tag on table without snapshot

[dramaticlly]

This fix help throw proper validation exception instead of NullPointerException when create branch or tag on iceberg table without any snapshot.

Before

Before
```scala
scala> val snapshotId = branchOptions.snapshotId.getOrElse(table.currentSnapshot().snapshotId())
java.lang.NullPointerException
  at $anonfun$res38$1(<console>:47)
  at scala.runtime.java8.JFunction0$mcJ$sp.apply(JFunction0$mcJ$sp.java:23)
  at scala.Option.getOrElse(Option.scala:189)
  ... 51 elided

After

scala> val snapshotId: java.lang.Long = branchOptions.snapshotId
          .orElse(Option(iceberg.table.currentSnapshot()).map(_.snapshotId()))
          .map(java.lang.Long.valueOf)
          .orNull
snapshotId: Long = null

CC @amogh-jahagirdar @zhangbutao

[Fokko]

LGTM, thanks for fixing this @dramaticlly

[Fokko]

@amogh-jahagirdar Would be great to get this into 1.3.0 as well

[amogh-jahagirdar]

Thanks @dramaticlly just a comment on the exception message. Agree @Fokko woul be great to get this in!

[amogh-jahagirdar]

Thanks @dramaticlly ! Will merge when CI completes

[zhangbutao]

I think this fix is the same idea I had before #7593. But it doesn't matter, I am glad to see it was fixed. Thanks. closing my previous pr.