Fixes support for 2d barcodes with RmagickOutputter

This commit fixes issues with RmagickOutputter and 2d barcodes. When using QrCode we were getting `non-conforming drawing primitive definition 'rectangle'` error messages from Rmagick. It seems to be caused by the 1px by 1px rectangles. This could probably use some specific tests as well, but it resolved our issue with it.