port from Pd Vanilla: assert table-sizes in tabread4~

tabread4~ needs at least 4 samples to interpolate;
this patch adds guards in order to not access out-of-bound indices in the table,
in case the table is smaller than 4 samples.
commit e667894370ec22bc1d1d844443d90f1a76adc03e

pd/src/d_array.c

@@ -298,6 +298,7 @@ static t_int *tabread_tilde_perform(t_int *w)
     int i;
     
     maxindex = x->x_npoints - 1;
+    if (maxindex < 0) goto zero;
     if (!buf) goto zero;
 
     for (i = 0; i < n; i++)
@@ -398,6 +399,7 @@ static t_int *tabread4_tilde_perform(t_int *w)
     int i;
     
     maxindex = x->x_npoints - 3;
+    if (maxindex < 0) goto zero;
 
     if (!buf) goto zero;