Capability write ignored when bounds become unrepresentable

[kevin-brodsky-arm]

Assuming that C0 is a valid capability, it is possible to modify its address without invalidating it using e.g.

(gdb) set $pc0.l += 0x20000

However, if C0 has narrow bounds and such an increment would make its bounds unrepresentable, GDB will silently ignore the command. It would probably be better to allow the set operation to go through and invalidate the capability, optionally printing a warning. Presumably, the same situation may occur if manipulating the bounds by setting a new value for $pc0.u.