Initial fix was not fully working, because faulty
edge shared the same address as screen area. This
lead to screen freeing issues -- double free (which
was supressed by guarded allocation actually) but
also freed memory access when iterating via edges
to free them.
Solved by a small hack which removes edges with bad
vertices from edges list. This prevents double-free
and freed memory access cased by corrupted files we're
currently fixing. In other cases this tweak is likely
be harmless -- in worst case scenario it'll lead to
small memory leak, which is not as much lethal as
freed memory access.
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