Assembling b{cond}.w with negative hex value fails silently (ARM/thumb)

[pr0me]

Architecture: THUMB

Example: bne.w #0xfffffe9e

Expected outcome: "\x7f\xf4\x4d\xaf" Little Endian

Explanation: The u32 hex value '0xfffffe9e' is -358 in decimal. This is in range for conditional branches in THUMB mode when we assemble to a wide (4 byte) instruction (https://www.keil.com/support/man/docs/armasm/armasm_dom1361289863797.htm#!#dom1361289863797__b_instr_fn). Instead of outputting the expected byte sequence, keystone-engine fails silently and outputs an empty byte vector. I am using the Rust bindings but e.g. shell-storm.org, which is also based on keystone, shows the same behavior (failing to assemble). However, trying to assemble the instruction with the operand being supplied in decimal form succeeds.