shortcut all of Environment#process if @targets is empty

lib/rscons/environment.rb

@@ -171,12 +171,11 @@ module Rscons
     # When a block is passed to Environment.new, this method is automatically
     # called after the block returns.
     def process
+      unless @targets.empty?
         clean_target_paths!
         cache = Cache.instance
         cache.clear_checksum_cache!
         targets_processed = {}
-      unless @targets.empty?
-        begin
         process_target = proc do |target|
           targets_processed[target] ||= begin
             @targets[target][:sources].each do |src|
@@ -195,6 +194,7 @@ module Rscons
             result
           end
         end
+        begin
           @targets.each do |target, target_params|
             process_target.call(target)
           end