mm macro .S interferes with .ne command, causing stack-overflow

[Jim Avera]

Hello,

There seems to be a bug in either the mm macros or gtroff itself,
where if the .S directive is used to change the vertical spacing after
a .ne command, then if the text adds up to more than one page-length an
abort occurs with

   fatal error: input stack limit exceeded (probable infinite loop)

Using the built-in .vs command instead of .S does not cause the problem,
so something else in the .S macro is triggering the bug.   From a brief
inspection of the m.tmac file, it might be related to resetting the
page-length trap.

I got this using Fedora Core 7 (gtroff version 1.18.1.4).

Here is a test case:

#!/bin/sh
groff -mm -Tps <<'EOF'
.ne 24v
.P
.S C +10
.nf
blah 1
blah 2
blah 3
blah 4
blah 5
blah 6
blah 7
blah 8
blah 9
blah 10
blah 11
blah 12
blah 13
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blah 31
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blah 37
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blah 60
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blah 70
EOF