replay: Improve assert in replay_char_read_all_load()

In replay_char_read_all_load() we get a buffer and size from the
replay log.  We know the size has to fit an int because of how we
write the log.  However the way we assert this is wrong: we cast the
size_t from replay_get_array() to an int and then check that it is
non-negative.  This misses cases where an over-large size is
truncated into a positive value by the cast.

Replace the assertion with checking that the size is in-range
before doing the cast.

Coverity complained about the possible overflow: CID 1643440.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20251124173407.50124-1-peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

replay/replay-char.c

@@ -126,8 +126,8 @@ int replay_char_read_all_load(uint8_t *buf)
         int res;
         replay_get_array(buf, &size);
         replay_finish_event();
+        assert(size <= INT_MAX);
         res = (int)size;
-        assert(res >= 0);
         return res;
     } else if (replay_next_event_is(EVENT_CHAR_READ_ALL_ERROR)) {
         int res = replay_get_dword();