When accessing an undefined number register, define it to be zero, like

the previous commit for strings and macros, only technically simpler.
Desired behaviour also mentioned by Werner Lemberg in 2011.
This diff adds functionality but is -21 +19 LOC.  :-)

1 files changed, 21 insertions, 0 deletions

diff --git a/regress/roff/nr/undef.out_ascii b/regress/roff/nr/undef.out_ascii
new file mode 100644
index 00000000..e7649eca
--- /dev/null
+++ b/regress/roff/nr/undef.out_ascii
@@ -0,0 +1,21 @@
+NR-UNDEF(1)                 General Commands Manual                NR-UNDEF(1)
+
+
+
+NNAAMMEE
+       nr-undef - using an undefined number register
+
+DDEESSCCRRIIPPTTIIOONN
+       The myr register is initially undefined.
+
+       Its initial value is 0.
+
+       After interpolating it, is is now defined.
+
+       After defining it to 1, it is of course still defined.
+
+       After removing it, it is again undefined.
+
+
+
+OpenBSD                          April 9, 2018                     NR-UNDEF(1)