avcodec/flicvideo: Make line_packets int

Fixes: signed integer overflow: -32768 * 196032 cannot be represented in type 'int'
Fixes: 15300/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FLIC_fuzzer-5733319519502336

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 54bd47f861)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/flicvideo.c

@@ -175,7 +175,7 @@ static int flic_decode_frame_8BPP(AVCodecContext *avctx,
     int lines;
     int compressed_lines;
     int starting_line;
-    signed short line_packets;
+    int line_packets;
     int y_ptr;
     int byte_run;
     int pixel_skip;
@@ -274,7 +274,7 @@ static int flic_decode_frame_8BPP(AVCodecContext *avctx,
                     break;
                 if (y_ptr > pixel_limit)
                     return AVERROR_INVALIDDATA;
-                line_packets = bytestream2_get_le16(&g2);
+                line_packets = sign_extend(bytestream2_get_le16(&g2), 16);
                 if ((line_packets & 0xC000) == 0xC000) {
                     // line skip opcode
                     line_packets = -line_packets;
@@ -508,7 +508,7 @@ static int flic_decode_frame_15_16BPP(AVCodecContext *avctx,
 
     int lines;
     int compressed_lines;
-    signed short line_packets;
+    int line_packets;
     int y_ptr;
     int byte_run;
     int pixel_skip;
@@ -572,7 +572,7 @@ static int flic_decode_frame_15_16BPP(AVCodecContext *avctx,
                     break;
                 if (y_ptr > pixel_limit)
                     return AVERROR_INVALIDDATA;
-                line_packets = bytestream2_get_le16(&g2);
+                line_packets = sign_extend(bytestream2_get_le16(&g2), 16);
                 if (line_packets < 0) {
                     line_packets = -line_packets;
                     if (line_packets > s->avctx->height)
@@ -806,7 +806,7 @@ static int flic_decode_frame_24BPP(AVCodecContext *avctx,
 
     int lines;
     int compressed_lines;
-    signed short line_packets;
+    int line_packets;
     int y_ptr;
     int byte_run;
     int pixel_skip;
@@ -870,7 +870,7 @@ static int flic_decode_frame_24BPP(AVCodecContext *avctx,
                     break;
                 if (y_ptr > pixel_limit)
                     return AVERROR_INVALIDDATA;
-                line_packets = bytestream2_get_le16(&g2);
+                line_packets = sign_extend(bytestream2_get_le16(&g2), 16);
                 if (line_packets < 0) {
                     line_packets = -line_packets;
                     if (line_packets > s->avctx->height)