Avoid generate @Delegate method body NPE

[eeoun]

Avoid generate @DeleGate method body NPE when deletegate target is null on javac's HandleDelegate

Add a null check before delegate call,now is only for javac

before:

    @Generated
    public void asd() {
        this.getSd().asd();
    }

    @Generated
    public String getExt() {
        return this.getSd().getExt();
    }

    @Generated
    public void setExt(final String ext) {
        this.getSd().setExt(ext);
    }

after

    @Generated
    public void asd() {
        if (this.getSd() != null) {
            this.getSd().asd();
        }
    }

    @Generated
    public String getExt() {
        return this.getSd() == null ? null : this.getSd().getExt();
    }

    @Generated
    public void setExt(final String ext) {
        if (this.getSd() != null) {
            this.getSd().setExt(ext);
        }
    }

[eeoun]

There is also e ecj's implement version. But i've not ever test event compile it. But I think it's ok. I'll add in PR if you think is ok.

commit 4d4e70b8c4b570740dac35cd45d2ef5aab821eeb