Fix startAt, endAt, equalTo optional 2nd params on Android

Author: BlooJeans

android/src/main/java/io/fullstack/firestack/FirestackDatabase.java

@@ -641,23 +641,23 @@ private Query getDatabaseQueryAtPathAndModifiers(
         query = query.limitToFirst(limit);
       } else if (methStr.contains("equalTo")) {
         String value = strArr[1];
-        String key = strArr[2];
+        String key = strArr.length >= 3 ? strArr[2] : null;
         if (key == null) {
           query = query.equalTo(value);
         } else {
           query = query.equalTo(value, key);
         }
       } else if (methStr.contains("endAt")) {
         String value = strArr[1];
-        String key = strArr[2];
+        String key = strArr.length >= 3 ? strArr[2] : null;
         if (key == null) {
           query = query.endAt(value);
         } else {
           query = query.endAt(value, key);
         }
       } else if (methStr.contains("startAt")) {
         String value = strArr[1];
-        String key = strArr[2];
+        String key = strArr.length >= 3 ? strArr[2] : null;
         if (key == null) {
           query = query.startAt(value);
         } else {