Simplify inet/cidr array type conversion

In spg__col_value, allow overridding of inet/cidr type conversion
using conversion procs.  Use goto to jump to the default case if
a conversion proc is set for the array type.

In spg__array_col_value, use convertor argument, and fallthrough
to keep things simpler and avoid encoding issues.  The fallthrough
will probably not happen in the typical case due to changes in
spg__col_value, but if parse_pg_array is called directly, it
probably could be reached.

ext/sequel_pg/sequel_pg.c

@@ -872,8 +872,6 @@ static VALUE spg_fetch_rows_set_cols(VALUE self, VALUE ignore) {
 
 static VALUE spg__array_col_value(char *v, size_t length, VALUE converter, int enc_index, int oid, VALUE db) {
   VALUE rv;
-  VALUE conv_procs = 0;
-  VALUE conversion_proc = 0;
   struct spg_blob_initialization bi;
 
   switch(oid) {
@@ -933,17 +931,10 @@ static VALUE spg__array_col_value(char *v, size_t length, VALUE converter, int e
       break;
     case 869: /* inet */
     case 650: /* cidr */
-      if (conv_procs == 0) {
-        conv_procs = rb_funcall(rb_funcall(db, spg_id_db, 0), spg_id_conversion_procs, 0);
-      }
-      conversion_proc = rb_funcall(conv_procs, spg_id_get, 1, INT2NUM(oid));
-      if (conversion_proc != Qnil) {
-        rv = rb_tainted_str_new(v, length);
-        rv = rb_funcall(conversion_proc, spg_id_call, 1, rv);
-      } else {
+      if (!RTEST(converter)) {
         rv = spg_inet(v, length);
+        break;
       }
-      break;
     default:
       rv = rb_tainted_str_new(v, length);
       PG_ENCODING_SET_NOCHECK(rv, enc_index);
@@ -1227,10 +1218,16 @@ static VALUE spg__col_value(VALUE self, PGresult *res, long i, long j, VALUE* co
             scalar_oid = 22;
             break;
           case 1041:
+            if (RTEST(colconvert[j])) {
+              goto default_cond;
+            }
             array_type = spg_sym_inet;
             scalar_oid = 869;
             break;
           case 651:
+            if (RTEST(colconvert[j])) {
+              goto default_cond;
+            }
             array_type = spg_sym_cidr;
             scalar_oid = 650;
             break;
@@ -1244,6 +1241,7 @@ static VALUE spg__col_value(VALUE self, PGresult *res, long i, long j, VALUE* co
           break;
         }
       default:
+      default_cond:
         rv = rb_tainted_str_new(v, PQgetlength(res, i, j));
         PG_ENCODING_SET_NOCHECK(rv, enc_index);
         if (colconvert[j] != Qnil) {