refactoring: if there is only one data for the median just return that one

src/average_median/average_median.c

@@ -23,6 +23,9 @@ double median(double *data, int n) {
       if (n==0) {
         return 0;
     }
+    else if (n==1){
+        return data[0];
+    }
     else if (n % 2 == 0) {
         return (data[n / 2 - 1] + data[n / 2]) / 2.0;
     } else {