Added conditional for default scaling of images.

(cherry picked from commit 6a0ff6f0f76a92a25c9cbbc315d3d7d11d1d7720)

lib/paperclip/thumbnail.rb

@@ -63,7 +63,8 @@ module Paperclip
     # into the thumbnail.
     def transformation_command
       scale, crop = @current_geometry.transformation_to(@target_geometry, crop?)
-      trans = "-resize \"#{scale}\""
+      trans = ""
+      trans << " -resize \"#{scale}\"" unless scale.blank?
       trans << " -crop \"#{crop}\" +repage" if crop
       trans << " #{convert_options}" if convert_options?
       trans

test/thumbnail_test.rb

@@ -178,6 +178,18 @@ class ThumbnailTest < Test::Unit::TestCase
         end
       end      
     end
+    
+    context "being thumbnailed with a blank geometry string" do
+      setup do
+        @thumb = Paperclip::Thumbnail.new(@file,
+                                          :geometry        => "",
+                                          :convert_options => "-gravity center -crop \"300x300+0-0\"")
+      end
+      
+      should "not get resized by default" do
+        assert_no_match(/-resize/, @thumb.transformation_command)
+      end
+    end
   end
 
   context "A multipage PDF" do