avcodec/jpeg2000: Check stepsize before using it

Fixes: value 1.87633e+10 is outside the range of representable values of type 'int'
Fixes: Undefined behavior
Fixes: 14246/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_JPEG2000_fuzzer-5758393601490944

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

libavcodec/jpeg2000.c

@@ -247,6 +247,11 @@ static void init_band_stepsize(AVCodecContext *avctx,
         }
     }
 
+    if (band->f_stepsize > (INT_MAX >> 15)) {
+        band->f_stepsize = 0;
+        av_log(avctx, AV_LOG_ERROR, "stepsize out of range\n");
+    }
+
     band->i_stepsize = band->f_stepsize * (1 << 15);
 
     /* FIXME: In OpenJPEG code stepsize = stepsize * 0.5. Why?