osc: fix cache displaying 60s in some cases

It was caused by string.format rounding e.g. 59.9 to 60.

player/lua/osc.lua

@@ -2095,10 +2095,10 @@ function osc_init()
             dmx_cache = state.dmx_cache
         end
         local min = math.floor(dmx_cache / 60)
-        local sec = dmx_cache % 60
+        local sec = math.floor(dmx_cache % 60) -- don't round e.g. 59.9 to 60
         return "Cache: " .. (min > 0 and
             string.format("%sm%02.0fs", min, sec) or
-            string.format("%3.0fs", dmx_cache))
+            string.format("%3.0fs", sec))
     end
 
     -- volume