Print at least one space between SYSCALL(ARGS) and = RESULT if tracee is killed

We already do it in the normal case, but in rare code path where
tracee is gone (SIGKILLed?) sometimes we were printing this:
"SYSCALL(ARGS <unavailable>)= ? <unavailable>" - note jammed together ")=".
test/sigkill_rain.c can be used to verify the fix.

* strace.c (printleader): add a space after ")" in " <unavailable>)"

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/strace.c b/strace.c
index fcdb37e..d5579d3 100644
--- a/strace.c
+++ b/strace.c
@@ -2953,7 +2953,7 @@
 	if (tcp_last) {
 		if (tcp_last->ptrace_errno) {
 			if (tcp_last->flags & TCB_INSYSCALL) {
-				tprintf(" <unavailable>)");
+				tprintf(" <unavailable>) ");
 				tabto(acolumn);
 			}
 			tprintf("= ? <unavailable>\n");