fixed GetCharCount method and tests

Author: petesramek

src/PolylineAlgorithm/PolylineEncoding.cs

@@ -223,9 +223,9 @@ public static int Normalize(double value, CoordinateValueType type) {
     /// <returns>
     /// The number of characters required to represent the <paramref name="variance"/> value, based on its magnitude.
     /// </returns>
-
     public static int GetCharCount(int variance) {
-        int rem = variance << 1;
+        long rem = (long)variance << 1;
+
         if (variance < 0) {
             rem = ~rem;
         }

tests/PolylineAlgorithm.Tests/PolylineEncodingTest.cs

@@ -101,8 +101,8 @@ public class PolylineEncodingTest {
         (-16777216,5),
         (16777216,6),
         (-16777217,6),
-        (int.MaxValue,6),
-        (int.MinValue,6),
+        (int.MaxValue,7),
+        (int.MinValue,7),
     ];
 
     #endregion