always set exit code

src/bun.js/api/bun/subprocess.zig

@@ -1480,6 +1480,9 @@ pub const Subprocess = struct {
 
                 if (std.os.W.IFSIGNALED(result.status)) {
                     this.signal_code = @intToEnum(SignalCode, @truncate(u8, std.os.W.TERMSIG(result.status)));
+                    if (this.exit_code == null) {
+                        this.exit_code = 1;
+                    }
                 } else if (std.os.W.IFSTOPPED(result.status)) {
                     this.signal_code = @intToEnum(SignalCode, @truncate(u8, std.os.W.STOPSIG(result.status)));
                 }