Undo NULL file protection in 1990/dds

As part of the redefinition of INABIAF the NULL file protection was
removed. The bus error fix, the erroneous prototype to fopen() and the
fgets() fix are still applied as these allow the entry to work properly
(and without an obnoxious warning at compile, linking or runtime about
gets()).

1990/dds/dds.c

@@ -17,7 +17,7 @@ X'R':B[2]!='M'&&(l=*--C)X'I':B[1]=='N'?fgets(p=B,R,stdin),P[*d]=S():(*(q=Q(B,"TH
 ()))X'G':p=B+4,B[2]=='S'&&(*C++=l,p++),l=S()-1 X'F':*(q=Q(B,"TO"))=0;p=B+5;P[i
 =B[3]]=S();p=q+2;M[i]=S();L[i]=l X'N':++P[*d]<=M[*d]&&(l=L[*d]);}else p=B+2,P[
 *B]=S();l++;}X'L':N printf(I)X'N':N(free(m[i]),0),m[i]=0	X'B':_ 0 t('S',5,"w",N
-f&&fprintf(f,I))t('O',4,"r",while(f&&fgets(B,R,f))(*Q(B,"\n")=0,G()))X 0:default:G()
+fprintf(f,I))t('O',4,"r",while(fgets(B,R,f))(*Q(B,"\n")=0,G()))X 0:default:G()
 ;}_ 0;}G(){l=atoi(B);m[l]&&(free(m[l]),0);(p=Q(B," "))?strcpy(m[l]=malloc(strlen(p
 )),p+1):(m[l]=0,0);}O(S,J,'=',==,'#',!=)O(J,K,'<',<,'>',>)O(K,V,'$',<=,'!',>=)
 O(V,W,'+',+,'-',-)O(W,Y,'*',*,'/',/)Y(){int o;_*p=='-'?p++,-Y():*p>='0'&&*p<=