Sev mean calculation could be nan

sev/lib/sev/src/sev_db_tree.cpp

@@ -311,13 +311,14 @@ pwr_tStatus sev_db::tree_update_value(int item_idx, int attr_idx, pwr_tTime time
       prev_deviation = 0;
     }
 
+    if (!feqf(scantime, 0.0f)) {
       m_items[item_idx].mean_value
         = (value * scantime
 	   + m_items[item_idx].mean_value * m_items[item_idx].mean_acc_time)
 	/ (scantime + m_items[item_idx].mean_acc_time);
       m_items[item_idx].mean_acc_time += scantime;
       m_items[item_idx].variance_acc
-        = prev_deviation * (value - m_items[item_idx].mean_value);
+        = fabs(prev_deviation * (value - m_items[item_idx].mean_value));
       m_items[item_idx].variance_cnt++;
 
       if (m_items[item_idx].mean_acc_time
@@ -335,5 +336,6 @@ pwr_tStatus sev_db::tree_update_value(int item_idx, int attr_idx, pwr_tTime time
 	m_items[item_idx].variance_cnt = 0;
       }
     }
+  }
   return SEV__SUCCESS;
 }