Fixup 2 for MDEV-18478 ANALYZE for statement part#2

We may get r_index_rows=0. Do not divide by 0 in this case,
as the result is undefined. Produce "r_total_filtered": 100 instead.

mysql-test/main/rowid_filter_myisam.result

@@ -686,7 +686,7 @@ ANALYZE
           "r_other_time_ms": "REPLACED",
           "r_engine_stats": REPLACED,
           "filtered": 8.529999733,
-          "r_total_filtered": 0,
+          "r_total_filtered": 100,
           "index_condition": "t1.nm like '3400%' or t1.nm like '3402%' or t1.nm like '3403%' or t1.nm like '3404%' or t1.nm like '3405%' or t1.nm like '3406%' or t1.nm like '3407%' or t1.nm like '3409%' or t1.nm like '3411%' or t1.nm like '3412%' or t1.nm like '3413%' or t1.nm like '3414%' or t1.nm like '3415%' or t1.nm like '3416%' or t1.nm like '3417%' or t1.nm like '3418%' or t1.nm like '3419%' or t1.nm like '3421%' or t1.nm like '3422%' or t1.nm like '3423%' or t1.nm like '3424%' or t1.nm like '3425%' or t1.nm like '3426%' or t1.nm like '3427%' or t1.nm like '3428%' or t1.nm like '3429%' or t1.nm like '3430%' or t1.nm like '3431%' or t1.nm like '3432%' or t1.nm like '3433%' or t1.nm like '3434%' or t1.nm like '3435%' or t1.nm like '3436%' or t1.nm like '3437%' or t1.nm like '3439%' or t1.nm like '3440%' or t1.nm like '3441%' or t1.nm like '3442%' or t1.nm like '3443%' or t1.nm like '3444%' or t1.nm like '3445%' or t1.nm like '3446%' or t1.nm like '3447%' or t1.nm like '3448%'",
           "r_icp_filtered": 100,
           "attached_condition": "t1.fl2 = 0",

sql/sql_explain.cc

@@ -2071,6 +2071,7 @@ void Explain_table_access::print_explain_json(Explain_query *query,
     writer->add_member("rows").add_ull(rows);
 
   double r_index_rows; /* protected by have_icp_or_rowid_filter */
+  bool r_index_rows_is_zero; /* also protected by have_icp_or_rowid_filter */
   bool have_icp_or_rowid_filter= false;
   /* `r_index_rows` and `r_rows` */
   if (is_analyze)
@@ -2092,13 +2093,17 @@ void Explain_table_access::print_explain_json(Explain_query *query,
         Pushed Index Condition is checked before checking the Rowid Filter, 
         so try getting it first.
       */
-      r_index_rows= file->handler_stats->icp_attempts / loops;
+      ulonglong val= file->handler_stats->icp_attempts;
+      r_index_rows_is_zero= (val == 0);
+      r_index_rows= val / loops;
       have_icp_or_rowid_filter= true;
     }
     else if (rowid_filter)
     {
       /* If ICP wasn't used, get the number from Rowid Filter */
-      r_index_rows= rowid_filter->tracker->get_container_lookups() / loops;
+      uint val= rowid_filter->tracker->get_container_lookups();
+      r_index_rows_is_zero= (val == 0);
+      r_index_rows= val / loops;
       have_icp_or_rowid_filter= true;
     }
 
@@ -2181,7 +2186,10 @@ void Explain_table_access::print_explain_json(Explain_query *query,
       else
         out_rows= tracker.get_avg_rows_after_where();
 
-      r_total_filtered= out_rows* 100.0 / r_index_rows;
+      if (r_index_rows_is_zero)
+        r_total_filtered= 100.0;
+      else
+        r_total_filtered= out_rows* 100.0 / r_index_rows;
     }
     else if (have_r_filtered)
       r_total_filtered= r_filtered;