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

contrib/one-true-awk/lib.c

@@ -62,6 +62,7 @@ void recinit(unsigned int n)
 	  || (fldtab = (Cell **) malloc((nfields+1) * 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");