render: Fix spanned width distribution for cells not at top or left.
[pspp] / tests / language /
drwxr-xr-x   ..
-rw-r--r-- 3376 command.at
drwxr-xr-x - commands
drwxr-xr-x - expressions
drwxr-xr-x - lexer
-rw-r--r-- 6006 mann-whitney.txt