vcl: only use default windows' GL Context for bitmaps if NULL / uninitialized.
vcl: only use default windows' GL Context for bitmaps if NULL / uninitialized.

Change-Id: I6465c548ba5d50da2cca7cce24e9bd2a20b28f47

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core