JVMDI spec: PopFrame JVMDI_ERROR_OPAQUE_FRAME clarify: applies to caller too

PopFrame disallows popping a frame which will return you to a caller which
is native:

Native frames may not be popped, nor may a Java frame be popped if
its caller is native code.

The error code for this:

JVMDI_ERROR_OPAQUE_FRAME
frame is a native frame.

Does not explicitly state that this includes the caller frame too