avcodec/gifdec: factorize interleave end handling out
also change it to a loop
Fixes out of array access
Fixes: asan_heap-oob_ca5410_8_asan_heap-oob_ca5410_97_ID_LSD_Size_Less_Then_Data_Inter_3.gif
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 8f1457864b)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
			
			
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		@@ -253,26 +253,21 @@ static int gif_read_image(GifState *s)
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            case 1:
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                y1 += 8;
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                ptr += linesize * 8;
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                if (y1 >= height) {
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                    y1 = pass ? 2 : 4;
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                    ptr = ptr1 + linesize * y1;
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                    pass++;
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                }
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                break;
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            case 2:
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                y1 += 4;
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                ptr += linesize * 4;
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                if (y1 >= height) {
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                    y1 = 1;
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                    ptr = ptr1 + linesize;
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                    pass++;
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                }
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                break;
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            case 3:
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                y1 += 2;
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                ptr += linesize * 2;
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                break;
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            }
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            while (y1 >= height) {
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                y1 = 4 >> pass;
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                ptr = ptr1 + linesize * y1;
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                pass++;
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            }
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        } else {
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            ptr += linesize;
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        }
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