fwts: segfaults on --disassemble-aml with some ACPI tables.

Commit d4fcca77cc3536a475e558492d65e1f063cdbabe in the ACPICA library introduced a regression which causes the segfault.

Looking at the same acpica core built into the iasl tool we can reproduce this fault:

Program received signal SIGSEGV, Segmentation fault.
0x000000000043867e in AcpiDmFieldPredefinedDescription (Op=0x7bbcc0)
    at ../../../source/components/disassembler/dmopcode.c:334
334 if (ACPI_COMPARE_NAME (Tag, Info->Name))
(gdb) print Tag
$1 = 0x0
(gdb) print Info->Name
$2 = 0x49d060 "_ACx"
(gdb)

Patch from Robert Moore at Intel fixes this:

diff --git a/source/common/dmrestag.c b/source/common/dmrestag.c
index 9afaad3..3097f15 100644
--- a/source/common/dmrestag.c
+++ b/source/common/dmrestag.c
@@ -541,6 +541,11 @@ AcpiDmCheckResourceReference (
     /* Get the Index term, must be an integer constant to convert */

     IndexOp = BufferNameOp->Common.Next;
+
+ /* Major cheat: The Node field is also used for the Tag ptr. Clear it now */
+
+ IndexOp->Common.Node = NULL;
+
     OpInfo = AcpiPsGetOpcodeInfo (IndexOp->Common.AmlOpcode);
     if (OpInfo->ObjectType != ACPI_TYPE_INTEGER)
     {
diff --git a/source/components/disassembler/dmopcode.c b/source/components/disassembler/dmopcode.c
index c3771b5..342e861 100644
--- a/source/components/disassembler/dmopcode.c
+++ b/source/components/disassembler/dmopcode.c
@@ -326,6 +326,10 @@ AcpiDmFieldPredefinedDescription (
     /* Major cheat: We previously put the Tag ptr in the Node field */

     Tag = ACPI_CAST_PTR (char, IndexOp->Common.Node);
+ if (!Tag)
+ {
+ return;
+ }

     /* Match the name in the info table */