Python access to RasterSource doesn't expose JVM errors

[vpipkt]

See #263 and #266

Trying to take actions on these dataframes may result in a JVM stack trace with ERROR message that does not get to the JVM user. PYthon user just gets for example 0 count or empty list from a take

[vpipkt]

Also see #319 and #174, those issues also expose this issue.