Apply r323963 from FreeBSD (pulling in the fix from OpenBSD)

| Fix uninitialized variable
|
| echo | awk 'BEGIN {i=$1; print i}' prints a boatload of stack
| garbage. NUL terminate the memory returned from malloc to prevent it.
|
| Obtained from: OpenBSD run.c 1.40
| Sponsored by: Netflix
| Differential Revision: https://reviews.freebsd.org/D12379
diff --git a/lib.c b/lib.c
index 00359ac..7e83439 100644
--- a/lib.c
+++ b/lib.c
@@ -62,6 +62,7 @@
 	  || (fldtab = (Cell **) malloc((nfields+2) * sizeof(Cell *))) == NULL
 	  || (fldtab[0] = (Cell *) malloc(sizeof(Cell))) == NULL )
 		FATAL("out of space for $0 and fields");
+	*record = '\0';
 	*fldtab[0] = dollar0;
 	fldtab[0]->sval = record;
 	fldtab[0]->nval = tostring("0");