[LocalPod] Fix for nasty bug related to Rake::FileList.

If the paths of the pod are resolved when the directory is not
created, FileList will cache no files and not update subsequently.

lib/cocoapods/dependency.rb

@@ -137,7 +137,7 @@ module Pod
           else
             copy_external_source_into_sandbox(sandbox)
             local_pod = sandbox.installed_pod_named(name, platform)
-            local_pod.clean if config.clean?
+            local_pod.clean if config.clean? && local_pod.exists?
             local_pod.top_specification
           end
         end

lib/cocoapods/local_pod.rb

@@ -204,6 +204,8 @@ module Pod
     end
 
     def expanded_paths(patterns, options = {})
+      raise Informative, "[Local Pod] Attempt to resolve paths for non existent pod." unless exists?
+
       patterns = [ patterns ] if patterns.is_a? String
       patterns.map do |pattern|
         pattern = root + pattern

spec/unit/local_pod_spec.rb

@@ -74,6 +74,11 @@ describe Pod::LocalPod do
     it "returns the platform" do
       @pod.platform.should == :ios
     end
+
+    it "raises if the files are accessed before creating the pod dir" do
+      @pod.implode
+      lambda { @pod.source_files }.should.raise Pod::Informative
+    end
   end
 
   describe "with installed source," do