#2610 smooth mcsplines w table crashes

[Karl Ratzsch]

For some reason, the combination of smooth mcsplines and plotting style "tables" leads to a crash.

$dat << EOD
1
3
7
5
5
EOD

set table
plot $dat us 0:1 smo mcsplines w table

Other smoothing options are OK, and also no crash without "w tables"

[Tatsuro MATSUOKA]

I cannot reproduce the crash on 6.1 on MinGW, Cygwin and Ubuntu(WSL).