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
Prevent invalid frame durations

Prevent frame duration from being negative when
exporting movie studio project

Change-Id: I459fb243650c777c2b59d1094acc88c3a944bd81
Avoid invalid memory access when using extractMetadata()

BpMediaMetadataRetriever::extractMetadata() returns a string
which is returned by readCString() function of the reply parcel object.
However, the parcel object is destroyed at the end of the
extractMetadata() function, and so the returned pointer is invalid.
This patch fixes this problem by storing the metadata string value.

Change-Id: I2a2ccba78246175b2845a237679d6cebe881e83b
Signed-off-by: Sangkyu Lee <sk82.lee@lge.com>