8028792: (ch) Channels native code needs to be checked for methods calling JNI with pending excepitons
Summary: added null checks to JNI functoin call return values
Reviewed-by: chegar, coffeys

Reviewed-by: alanb

Reviewed-by: chegar, ksrini

Reviewed-by: chegar, coffeys

Reviewed-by: coffeys, chegar

Reviewed-by: xdono

Summary: Avoid *Critical; fix compile warnings; improve readability
Reviewed-by: alanb

Reviewed-by: darcy, weijun