BITCOUNT Upper bound calculation fix (#1138)

* fix endOffset calculation

* add test for out of bound bitcount offset

Author: vazois

libs/server/Resp/Bitmap/BitmapManagerBitCount.cs

@@ -70,7 +70,7 @@ public static long BitCountDriver(long startOffset, long endOffset, byte offsetT
             {
                 startOffset = startOffset < 0 ? ProcessNegativeOffset(startOffset, valLen) : startOffset;
                 endOffset = endOffset < 0 ? ProcessNegativeOffset(endOffset, valLen) : endOffset;
-                endOffset = endOffset >= valLen ? valLen : endOffset;
+                endOffset = endOffset >= valLen ? valLen - 1 : endOffset;
 
                 if (startOffset >= valLen) // If startOffset greater that valLen always bitcount zero
                     return 0;

test/Garnet.test/GarnetBitmapTests.cs

@@ -2314,6 +2314,9 @@ public void BitmapBitCountSimpleTest()
             long count = db.StringBitCount(key);
             ClassicAssert.AreEqual(26, count);
 
+            count = db.StringBitCount(key, 0, int.MaxValue);
+            ClassicAssert.AreEqual(26, count);
+
             count = db.StringBitCount(key, 0, 0);
             ClassicAssert.AreEqual(4, count);