avcodec/scpr: Check y in first line loop in decompress_i()

Fixes: out of array access
Fixes: 1478/clusterfuzz-testcase-minimized-5285486908145664

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/scpr.c

@@ -331,6 +331,9 @@ static int decompress_i(AVCodecContext *avctx, uint32_t *dst, int linesize)
         clr = (b << 16) + (g << 8) + r;
         k += run;
         while (run-- > 0) {
+            if (y >= avctx->height)
+                return AVERROR_INVALIDDATA;
+
             dst[y * linesize + x] = clr;
             lx = x;
             ly = y;