Update drouting.c

In weight_based_sort() function:

- Changed RAND_MAX to RAND_MAX + 1 to make sure that quotient is always less than 1
- Changed float to double to avoid rounding errors, particularly when the value of rand() nears RAND_MAX and thus the quotient could round to 1

(cherry picked from commit 6ef8168)

modules/drouting/drouting.c

@@ -2878,7 +2878,7 @@ static int weight_based_sort(pgw_list_t *pgwl, int size, unsigned short *idx)
 		}
 		if (weight_sum) {
 			/* randomly select number */
-			rand_no = (unsigned int)(weight_sum*((float)rand()/(float)RAND_MAX));
+			rand_no = (unsigned int)(weight_sum*((double)rand()/((double)RAND_MAX+1)));
 			LM_DBG("random number is %d\n",rand_no);
 			/* select the element */
 			for( i=first ; i<size ; i++ )
@@ -2895,7 +2895,7 @@ static int weight_based_sort(pgw_list_t *pgwl, int size, unsigned short *idx)
 			}
 		} else {
 			/* randomly select index */
-			//	i = (unsigned int)((size-first)*((float)rand()/RAND_MAX));
+			//	i = (unsigned int)((size-first)*((double)rand()/((double)RAND_MAX+1)));
 			i = first;
 		}
 		LM_DBG("selecting element %d with weight %d\n",