SRC: add speed test crash reproduce script

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

src/test-speed-crash.sh

+set -Eeo pipefail
+
+X=1
+while :
+do
+  echo "## $X"
+  audiowmark cmp test-speed-crash.wav f0 --detect-speed --test-speed 0.9764
+  X=$((X + 1))
+done

src/wmspeed.cc

@@ -87,6 +87,9 @@ public:
   Mags&
   operator() (int row, int col)
   {
+    assert (row >= 0 && row < m_rows);
+    assert (col >= 0 && col < m_cols);
+
     return m_data[row * m_cols + col];
   }
   void
@@ -259,6 +262,8 @@ SpeedSync::prepare_mags (const SpeedScanParams& scan_params)
               dmag += fft_out_db[sync_bit.down[i]];
             }
           sync_matrix (row, col++) = MagMatrix::Mags {umag, dmag};
+          assert (umag != 0);
+          assert (dmag != 0);
         }
       assert (col == n_sync_cols);
       row++;
@@ -293,6 +298,8 @@ SpeedSync::compare_bits (BitValue *bit_values, double relative_speed, int *start
 
       auto& bv = bit_values[si->bit];
       auto mags = sync_matrix (index, mi);
+      assert (mags.umag != 0);
+      assert (mags.dmag != 0);
       if (B2)
         {
           bv.umag += mags.dmag;