Fix memory leak in filterRRectToNine

Found by our valgrind bot:

63,808 bytes in 126 blocks are definitely lost in loss record 76 of 76
at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
by 0x52C126: sk_malloc_flags(unsigned long, unsigned int) (SkMemory_malloc.cpp:45)
by 0x52C157: sk_malloc_throw(unsigned long) (SkMemory_malloc.cpp:31)
by 0x42A9B2: SkMask::AllocImage(unsigned long) (SkMask.cpp:40)
by 0x5BD349: prepare_to_draw_into_mask(SkRect const&, SkMask*) (SkBlurMaskFilter.cpp:170)
by 0x5BEDC6: SkBlurMaskFilterImpl::filterRRectToNine(SkRRect const&, SkMatrix const&, SkIRect const&, SkMaskFilter::NinePatch*) const (SkBlurMaskFilter.cpp:181)
by 0x42B604: SkMaskFilter::filterRRect(SkRRect const&, SkMatrix const&, SkRasterClip const&, SkBounder*, SkBlitter*, SkPaint::Style) const (SkMaskFilter.cpp:218)
by 0x42460E: SkDraw::drawRRect(SkRRect const&, SkPaint const&) const (SkDraw.cpp:1056)
by 0x413F9C: SkBitmapDevice::drawRRect(SkDraw const&, SkRRect const&, SkPaint const&) (SkBitmapDevice.cpp:235)
by 0x419D31: SkCanvas::drawRRect(SkRRect const&, SkPaint const&) (SkCanvas.cpp:1695)
by 0x43F865: SkPicturePlayback::draw(SkCanvas&, SkDrawPictureCallback*) (SkPicturePlayback.cpp:1001)
by 0x43BC1A: SkPicture::draw(SkCanvas*, SkDrawPictureCallback*) (SkPicture.cpp:261)
by 0x407D42: void sk_tools::DrawTileToCanvas<SkPicture>(SkCanvas*, SkRect const&, SkPicture*) (PictureRenderer.cpp:502)
by 0x4080BA: sk_tools::TiledPictureRenderer::render(SkString const*, SkBitmap**) (PictureRenderer.cpp:546)
by 0x4064EF: render_picture(SkString const&, SkString const*, sk_tools::PictureRenderer&, SkBitmap**) (render_pictures_main.cpp:193)
by 0x406637: render_picture(SkString const&, SkString const*, sk_tools::PictureRenderer&) (render_pictures_main.cpp:251)
by 0x406F50: tool_main(int, char**) (render_pictures_main.cpp:360)
by 0x407142: main (render_pictures_main.cpp:455)

[scroggo, 2013-11-11 18:33:49]

lgtm

[robertphillips, 2013-11-11 19:24:45]

committed as r12222