Issue #521: Error: Can't create Seam Allowance after using Union Tool (dismine/valentina)

New issue 521: Error: Can’t create Seam Allowance after using Union Tool https://bitbucket.org/valentinateam/valentina/issues/521/error-cant-create-seam-allowance-after

Susan Spencer:

Ubuntu 14.04 64-bit Test Build v0.5.0.1285a build rev 01d47c22fd13

In Detail mode, can’t add a seam allowance after joining two pieces with Union Tool. The two pieces use the same points.