avcodec/aacsbr: Fix libavcodec/aacsbr.c:257:59: runtime error: division by zero

Fixes: 1882/clusterfuzz-testcase-minimized-5539735650959360

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Rostislav Pehlivanov <atomnuker@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/aacsbr.c

@@ -241,6 +241,7 @@ static void sbr_gain_calc(AACContext *ac, SpectralBandReplication *sbr,
                                             ((1.0f + sbr->e_curr[e][m]) *
                                              (1.0f + sbr->q_mapped[e][m])));
                 }
+                sbr->gain[e][m] += FLT_MIN;
             }
             for (m = sbr->f_tablelim[k] - sbr->kx[1]; m < sbr->f_tablelim[k + 1] - sbr->kx[1]; m++) {
                 sum[0] += sbr->e_origmapped[e][m];