This gets especially confusing if you start plugging in host addresses
from a trace and you wonder why the output keeps changing. Report when
read_memory_func fails instead of blindly disassembling the buffer
contents.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220929114231.583801-35-alex.bennee@linaro.org>