VML import: don't assume both parameters are available while parsing commands

The problematic path was "m,l21600,r,21600l,21600xem@1@0l@3@2nfe", here
"m,l" means an implicit "m0,0l", but only the first zero is in the
coords list. If the second is missing, assume 0 as well.

Change-Id: I03065e34c959103c9caf64271aa3ebbb7ad52726