bat: better fix for ACPI, from bioe007

Previous commit had redudant string > number conversions, and only
covered one scenario - when battery is charged. bioe007 suggested to
use math.min. Now lets explain why this is needed. Some (lousy)
batteries report "remaining capacity" higher than "last full capacity"
when AC is connected. That leads to battery charges like "160%".

bat.lua

@@ -7,7 +7,10 @@
 local tonumber = tonumber
 local io = { open = io.open }
 local setmetatable = setmetatable
-local math = { floor = math.floor }
+local math = {
+    min = math.min,
+    floor = math.floor
+}
 local string = {
     find = string.find,
     match = string.match,
@@ -60,12 +63,8 @@ local function worker(format, batid)
     local remaining = string.match(statefile, "remaining capacity:[%s]+([%d]+).*")
 
 
-    -- Calculate percentage
-    local percent = math.floor(remaining / capacity * 100)
-    local percent = string.format("%02d", percent)
-    -- Work around broken batteries and/or ACPI implementations
-    if state == "↯" and tonumber(percent) > 100 then percent = 100 end
-
+    -- Calculate percentage (but work around broken BAT/ACPI implementations)
+    local percent = math.min(math.floor(remaining / capacity * 100), 100)
 
     -- Calculate remaining (charging or discharging) time
     if state == "+" then