Keep empty fields and literal delimiters in strsplit

pfUI.api.strsplit (also the bare strsplit in module code) built a
"([^%s]+)" pattern from the delimiter. That dropped empty fields
("a,,b" gave "a", "b") despite the comment, and a delimiter that is a
pattern character (% ] ^ -) broke the pattern. It now scans for an
escaped character class and keeps every field, like WoW's strsplit.

The custom buff indicator list skips the empty entries this now yields
for "" and the list editor's leading "#", so an empty list no longer
scans auras.

api/api.lua

@@ -103,13 +103,20 @@ mod = math.mod or mod
 --                              characters (bytes) in the string.
 -- 'subject'    [string]        String to split.
 -- return:      [list]          a list of strings.
-local format, sgsub = string.format, string.gsub
+local sfind, ssub, sgsub = string.find, string.sub, string.gsub
 function pfUI.api.strsplit(delimiter, subject)
   if not subject then return nil end
-  local fields = {}
-  delimiter = delimiter or ":"
-  local pattern = format("([^%s]+)", delimiter)
-  sgsub(subject, pattern, function(c) fields[table.getn(fields)+1] = c end)
+  -- a character class of the delimiter bytes, each escaped so % ] ^ - stay
+  -- literal
+  local set = "[" .. sgsub(delimiter or ":", "(%W)", "%%%1") .. "]"
+  local fields, start = {}, 1
+  local pos = sfind(subject, set)
+  while pos do
+    table.insert(fields, ssub(subject, start, pos - 1))
+    start = pos + 1
+    pos = sfind(subject, set, start)
+  end
+  table.insert(fields, ssub(subject, start))
   return unpack(fields)
 end
 

api/unitframes.lua

@@ -1984,8 +1984,8 @@ function pfUI.uf:RefreshUnit(unit, component)
 
     if not unit.indicator_custom and unit.config.buff_indicator == "1" then
       unit.indicator_custom = {}
-      for k, v in pairs({strsplit("#", unit.config.custom_indicator)}) do
-        unit.indicator_custom[k] = v:lower()
+      for _, v in pairs({strsplit("#", unit.config.custom_indicator)}) do
+        if v ~= "" then table.insert(unit.indicator_custom, v:lower()) end
       end
     elseif not unit.indicator_custom then
       unit.indicator_custom = {}