add debug code for SH-207: viewer crash in LLVertexBuffer::mapBuffer
add debug code for SH-207: viewer crash in LLVertexBuffer::mapBuffer

gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm