Rebuild fields when NF is assigned to itself

bugs-fixed/README

@@ -23,3 +23,5 @@ and also if CONVFMT changed.
 
 7. unary-plus: Unary plus on a string constant returned the string.
 Instead, it should convert the value to numeric and give that value.
+
+X. nf-self-assign: "NF = NF" wouldn't force the record to be rebuilt.

bugs-fixed/nf-self-assign.awk

@@ -0,0 +1,6 @@
+BEGIN {
+	$0="a b c";
+	OFS=",";
+	NF = NF;
+	print;
+}

bugs-fixed/nf-self-assign.bad

@@ -0,0 +1 @@
+a b c

bugs-fixed/nf-self-assign.ok

@@ -0,0 +1 @@
+a,b,c

run.c

@@ -1117,8 +1117,8 @@ Cell *assign(Node **a, int n)	/* a[0] = a[1], a[0] += a[1], etc. */
 	y = execute(a[1]);
 	x = execute(a[0]);
 	if (n == ASSIGN) {	/* ordinary assignment */
-		if (x == y && !(x->tval & (FLD|REC)))	/* self-assignment: */
-			;		/* leave alone unless it's a field */
+		if (x == y && !(x->tval & (FLD|REC)) && x != nfloc)
+			;	/* self-assignment: leave alone unless it's a field or NF */
 		else if ((y->tval & (STR|NUM)) == (STR|NUM)) {
 			setsval(x, getsval(y));
 			x->fval = getfval(y);