Fix for crash if no content in DESCRIBE response

If DESCRIBE response is received with status 200 but no content,
MyHandler will still set content data for session description
parsing. This will cause NULL Pointer crash.
This fix checks whether DESCRIBE response has content before
parsing session description.

Change-Id: I114ae6fd54ce804e61718f62618ca9008425a433
Frameworks av: Small QCOM changes + corrections and cleanup

Change-Id: I513b93a1be0862a1b72e08790e4f87bacb1ef050