fix VAR=VAL loading from config

Author: Rich Whitcroft

lib/rex/parser/ini.rb

@@ -165,7 +165,12 @@ def read_groups_string(str) # :nodoc:
       # Is it a VAR=VAL?
       elsif (md = line.match(/^(.+?)=(.*)$/))
         if (active_group)
-          self[active_group][md[1]] = md[2]
+          var, val = md[1], md[2]
+
+          # don't clobber datastore nils with ""
+          unless val.empty?
+            self[active_group][var] = val
+          end
         end
       end
     }