i#1998: fix crash in release build dr_app_running_under_dynamorio
i#1998: fix crash in release build dr_app_running_under_dynamorio

The mangling for dr_app_running_under_dynamorio blindly sets an operand
without ensuring the instr is Level 3+.  We can't easily auto-up-decode for
set routines (the decoder uses them): only for get, so we explicitly do an
up-decode for this unusual mangling path.

Review-URL: https://codereview.appspot.com/306400043

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio