luci-app-statistics: fix prepare values from list vlaues

If UCI store values as a list instead of an option, conversation for the
collectd configuration is not work correctly. This is due to the use of
a DynamicList type element in the UI (for example, for the RRATimespans
field). For this function argument val receives as array instead of a
string, so no additional conversion is required.

Signed-off-by: Aleksey Kolosov <[email protected]>

applications/luci-app-statistics/root/usr/libexec/stat-genconfig

@@ -58,7 +58,7 @@ function parse_units(ustr) {
 
 const preprocess = {
 	RRATimespans: function(val) {
-		return join(' ', map(split(val, /\s+/), parse_units));
+		return join(' ', map(type(val) == 'array' ? val :  split(val, /\s+/), parse_units));
 	}
 };