Another correction to svn rev56509

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.

source/blender/blenloader/intern/readfile.c

@@ -6176,6 +6176,7 @@ static bool direct_link_screen(FileData *fd, bScreen *sc)
 		
 		if (se->v1 == NULL) {
 			printf("Error reading Screen %s... removing it.\n", sc->id.name+2);
+			BLI_remlink(&sc->edgebase, se);
 			wrong_id = true;
 		}
 	}