SSLSocket: restore previous pre-handshake behavior
SSLSocket: restore previous pre-handshake behavior

Before AppData was created in the initial handshake, calling SSL_read or
SSL_write would have a NULL appData field. This caused an exception to
be thrown. Now we have to check to make sure the handshake completed
before we continue on with SSL_read and SSL_write.

Change-Id: I969577cf56f61858450a7981a5196f58a6502968

google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt,google/conscrypt