[groff] Heirloom: text disappearing when output line trap + interrupted text

[Mircea Hossu]

Hello,

Before creating a bug report, I would like to verify that I am not
misunderstanding something and that this is indeed a bug. 

It appears that a word starting with a period or apostrophe is
interpreted as a request/macro call even if it does not start at the
beginning of the line, under the following combination: fill mode,
output line trap (\P) and text interruption (\c). This causes the word
and remainder of the line to disappear from the generated output.


Test doc:

.po 0
.ll 100p
.de M
.  tm M called
..

.\" (1) OK if word doesn't appear at line break:
AAA\PM\c
AAA BBB BBB BBB BBB .CCC CCC
DDD

.\" (2) If, by chance, word appears at line break
.\"     then word and remainder of line disappear.
AAA\PM\c
AAA BBB BBB BBB .CCC CCC
DDD

.\" (3) Expected output for (2) (removed \PM)
AAA\c
AAA BBB BBB BBB .CCC CCC
DDD


Generated output:

AAAAAA BBB BBB
BBB BBB .CCC CCC
DDD

AAAAAA BBB BBB
BBB DDD

AAAAAA BBB BBB
BBB .CCC CCC DDD