Fix segfault in 1990/dds

In all versions the program would segfault if the file could not be
opened as it would write/close the NULL FILE *. Now it doesn't act on
the file unless f != NULL. If it is it just does the usual of writing
'Ok' to stdout.

1990/dds/README.md

@@ -16,7 +16,8 @@ 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. Thank you Cody for your assistance!
+it safer. He also fixed a segfault in the case that the file cannot be loaded.
+Thank you Cody for your assistance!
 
 ### To run
 
@@ -32,9 +33,6 @@ Give the following lines as input:
 
 NOTE: this is case sensitive.
 
-NOTE: this program will likely segfault if you specify a file that cannot be
-opened.
-
 ## Judges' comments:
 
 

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
-fprintf(f,I))t('O',4,"r",while(fgets(B,R,f))(*Q(B,"\n")=0,G()))X 0:default:G()
+f&&fprintf(f,I))t('O',4,"r",while(f&&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<=