BaseMaster: Fix uint rollover

When a send till acknowledged message was recieved it would cause the
request count to roll over backwards and transmit for 255 times even if
the ack was received.

Author: cujomalainey

src/BaseClasses/ANTPLUS_BaseMasterProfile.cpp

@@ -41,7 +41,9 @@ bool BaseMasterProfile::isRequestedPagePending() {
 }
 
 uint8_t BaseMasterProfile::getRequestedPage() {
-    _requestedCount--;
+    if (_requestedCount > 0) {
+        _requestedCount--;
+    }
     return _requestedPage;
 }