Fix compiler warnings in modules/FvwmScript/Instructions.c

[pm215]

This pull request has a couple of simple commits that fix the following compiler warnings that I see with gcc (Debian 8.3.0-6) 8.3.0:

Instructions.c: In function ‘FuncGetOutput’:
Instructions.c:366:7: warning: ‘strncpy’ specified bound 255 equals destination size [-Wstringop-truncation]
       strncpy(Command,cmndbuf,255);
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
Instructions.c: In function ‘WriteToFile’:
    Instructions.c:1743:5: warning: passing argument 1 to restrict-qualified parameter aliases with argument 3 [-Wrestrict]
     sprintf(buf,"%s\n%s%d\n",buf,StrBegin,getpid());
     ^~~~~~~
Instructions.c:1744:5: warning: passing argument 1 to restrict-qualified parameter aliases with argument 3 [-Wrestrict]
     sprintf(buf,"%s%s",buf,arg[1]);
     ^~~~~~~
Instructions.c:1745:5: warning: passing argument 1 to restrict-qualified parameter aliases with argument 3 [-Wrestrict]
     sprintf(buf,"%s%s\n",buf,StrEnd);
     ^~~~~~~

I believe these to be genuine bugs, not just the compiler being over-enthusiastic. The caveat is that because I don't use FvwmScript myself I don't have any way of testing my fixes. I opted for the simplest changes that fix the bugs, retaining the old-school string handling rather than attempting any kind of rewrite to something less bug-prone. (My motivation for sending in this fix was mostly just as a warm-up task before I have a look into issue #409, which I've been running into.)

[ThomasAdam]

Hi @pm215

Thanks. This looks OK to me, although really we should be using xasprintf() instead. If you want to resend using that, fair enough, but it's not something I'm too fussed about either way.