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/README.md

@@ -16,7 +16,7 @@ you Yusuke!
 
 [Cody Boone Ferguson](/winners.html#Cody_Boone_Ferguson) removed the erroneous
 prototype to `fopen()` and made this use `fgets()` instead of `gets()` to make
-it safer. He also fixed a segfault in the case that the file cannot be loaded.
+it safer and to prevent a potentially alarming warning at linking or runtime.
 Thank you Cody for your assistance!
 
 ## To run

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<=