hg: jdk/sandbox: 8213795: Force explicit null check on patching placeholder offset

[chris.hegarty at oracle.com]

Changeset: f642ede2eb07
Author:    rkennke
Date:      2018-11-14 18:57 +0100
URL:       http://hg.openjdk.java.net/jdk/sandbox/rev/f642ede2eb07

8213795: Force explicit null check on patching placeholder offset
Reviewed-by: kvn, adinn

! src/hotspot/share/asm/assembler.cpp