fix #1098: dX cmds trunc out on x86 binaries

[disconnect3d]

Before:

pwndbg> hexdump $esp
+0000 0xffffd260  01 00 00 00  c8 d3 ff ff  00 00 00 00  da d3 ff ff  │....│....│....│....│
+0010 0xffffd270  ed d3 ff ff  d9 d9 ff ff  0b da ff ff  2d da ff ff  │....│....│....│-...│
+0020 0xffffd280  3c da ff ff  49 da ff ff  ff db ff ff  0f dc ff ff  │<...│I...│....│....│
+0030 0xffffd290  26 dc ff ff  34 dc ff ff  49 dc ff ff  51 dc ff ff  │&...│4...│I...│Q...│
pwndbg> dq $esp
ffffd260     0000000000000001 0000000000000000
ffffd270     00000000ffffd3ed 00000000ffffda0b
ffffd280     00000000ffffda3c 00000000ffffdbff
ffffd290     00000000ffffdc26 00000000ffffdc49

After:

pwndbg> hexdump $esp
+0000 0xffffd260  01 00 00 00  c8 d3 ff ff  00 00 00 00  da d3 ff ff  │....│....│....│....│
+0010 0xffffd270  ed d3 ff ff  d9 d9 ff ff  0b da ff ff  2d da ff ff  │....│....│....│-...│
+0020 0xffffd280  3c da ff ff  49 da ff ff  ff db ff ff  0f dc ff ff  │<...│I...│....│....│
+0030 0xffffd290  26 dc ff ff  34 dc ff ff  49 dc ff ff  51 dc ff ff  │&...│4...│I...│Q...│
pwndbg> dq $esp
ffffd260     ffffd3c800000001 ffffd3da00000000
ffffd270     ffffd9d9ffffd3ed ffffda2dffffda0b
ffffd280     ffffda49ffffda3c ffffdc0fffffdbff
ffffd290     ffffdc34ffffdc26 ffffdc51ffffdc49