acpi_battery: avoid divide-by-zero when no devices have capacity info

[jeffpc_josefsipek.net]

Summary

On laptops with builtin batteries, disconnecting the battery may show up as
a battery without any capacity information. (The theory is that one is
disconnecting the cells but the electronics identifying the battery are
still connected.) As a result, the loop over all batteries in
acpi_battery_get_battinfo results in total_lfcap == 0.

So, just check that total_lfcap is non-zero to avoid a division by zero
(triggerable by sysctl hw.acpi.battery).

Reported/tested by: Stefano Marinelli

[emaste]

sys/dev/acpica/acpi_battery.c

273

style(9) asks to avoid using non-booleans in a boolean context, so total_lfcap != 0 -- but then, we probably want total_lfcap > 0 since -ve values don't make sense. I'd also suggest an if-else like just above for valid_rate rather than the ternary op.

[jeffpc_josefsipek.net]

if-else, proper boolean comparison