Key comparison for RTDB queries should correctly handle boundary sentinels (#2328)

Author: jmwski

firebase-database/src/main/java/com/google/firebase/database/snapshot/ChildKey.java

@@ -71,9 +71,9 @@ protected int intValue() {
   public int compareTo(ChildKey other) {
     if (this == other) {
       return 0;
-    } else if (this == MIN_KEY || other == MAX_KEY) {
+    } else if (this.key.equals(MIN_KEY_NAME) || other.key.equals(MAX_KEY_NAME)) {
       return -1;
-    } else if (other == MIN_KEY || this == MAX_KEY) {
+    } else if (other.key.equals(MIN_KEY_NAME) || this.key.equals(MAX_KEY_NAME)) {
       return 1;
     } else if (this.isInt()) {
       if (other.isInt()) {