Fix bug with extension in "Save As..."
Fix bug with extension in "Save As..."

If project was saved with file dialog filter including several extensions
the result would be like "name.appleseed *.appleseedz".
Now it checks if there is only one extension and in case there are more
it just uses .appleseed extension.

aytekaman/appleseed,glebmish/appleseed,gospodnetic/appleseed,est77/appleseed,Aakash1312/appleseed,dictoon/appleseed,gospodnetic/appleseed,gospodnetic/appleseed,pjessesco/appleseed,Vertexwahn/appleseed,Biart95/appleseed,est77/appleseed,appleseedhq/appleseed,glebmish/appleseed,appleseedhq/appleseed,glebmish/appleseed,Biart95/appleseed,luisbarrancos/appleseed,dictoon/appleseed,est77/appleseed,Aakash1312/appleseed,luisbarrancos/appleseed,glebmish/appleseed,gospodnetic/appleseed,Biart95/appleseed,pjessesco/appleseed,pjessesco/appleseed,dictoon/appleseed,aytekaman/appleseed,Aakash1312/appleseed,est77/appleseed,Aakash1312/appleseed,Biart95/appleseed,Aakash1312/appleseed,appleseedhq/appleseed,Vertexwahn/appleseed,appleseedhq/appleseed,est77/appleseed,gospodnetic/appleseed,luisbarrancos/appleseed,glebmish/appleseed,dictoon/appleseed,pjessesco/appleseed,Vertexwahn/appleseed,Vertexwahn/appleseed,appleseedhq/appleseed,aytekaman/appleseed,Biart95/appleseed,luisbarrancos/appleseed,aytekaman/appleseed,luisbarrancos/appleseed,dictoon/appleseed,aytekaman/appleseed,Vertexwahn/appleseed,pjessesco/appleseed