spu: memory leak with spu_render_entry_t.scaled_region_pics

Direct leak of 80 byte(s) in 1 object(s) allocated from:
    #0 0x5634dcf42c15 in realloc (/home/tom/work/git/vlc/build-asan/bin/vlc-static+0xc9c15) (BuildId: 73e5e4135420437472a2f50436b5fa618e066aa8)
    #1 0x7fac849baf30 in vlc_reallocarray /home/tom/work/git/vlc/build-asan/src/../../include/vlc_common.h:1134:54
    #2 0x7fac849baf30 in vlc_vector_reallocdata_ /home/tom/work/git/vlc/build-asan/src/../../include/vlc_vector.h:171:15
    #3 0x7fac849baf30 in spu_entry_EnsureScaledSize /home/tom/work/git/vlc/build-asan/src/../../src/video_output/vout_subpictures.c:691:13
    #4 0x7fac849b6571 in spu_Render /home/tom/work/git/vlc/build-asan/src/../../src/video_output/vout_subpictures.c:2125:13
    #5 0x7fac849a550b in RenderSPUs /home/tom/work/git/vlc/build-asan/src/../../src/video_output/video_output.c:1122:12
    #6 0x7fac849a550b in PrerenderPicture /home/tom/work/git/vlc/build-asan/src/../../src/video_output/video_output.c:1277:23
    #7 0x7fac849a550b in RenderPicture /home/tom/work/git/vlc/build-asan/src/../../src/video_output/video_output.c:1303:15
    #8 0x7fac849a39e3 in DisplayPicture /home/tom/work/git/vlc/build-asan/src/../../src/video_output/video_output.c:1501:9
    #9 0x7fac849a39e3 in Thread /home/tom/work/git/vlc/build-asan/src/../../src/video_output/video_output.c:1825:20
    #10 0x5634dcf4050a in asan_thread_start(void*) asan_interceptors.cpp.o

Happening even with !4715 (940b3632) applied.